Resolving network license issues on client machines (Zemax Legacy)

Authored By Don Dickinson


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The article addresses common problems client machines have trying to find and use a Zemax network license for Opticstudio, OpticsBuilder, or OpticsViewer. It also covers common issues using the license "Check out" feature. It does not apply to Ansys issued licenses. 

Before getting started, please read! 

This article applies to software licensed via legacy Zemax licenses. Legacy Zemax licenses include all USB-based licenses, licenses with 5-digit numeric serial numbers (e.g. 22000), and 6-digit alpha-numeric serial numbers beginning with "L" or "T" (e.g. L100000). You can identify your license type using the guide located here: How to identify your legacy Zemax license.

If you are using Ansys versions of Zemax software, and get errors after configuring a  machine to find an Ansys license, see Solving errors when accessing an Ansys network license

If your organization uses a Black USB network license (these have a license number of 22000-40999), information on configuring the server and clients is located here.



For information on the first time configuration of your client machine to reach a Zemax license server, see "Configuring Zemax applications to access a Zemax network license".

See the topics on the right for common errors and prompts you may receive when trying to start the software, which will link directly to the issue you are having. 

Zemax password prompt


This occurs when you are trying to use a subscription license. These license types are indicated by an "Activated" checkbox in the License Manager. To use a subscription license, your MyZemax account must be authorized by your License Administrator. See the MyZemax FAQ for additional details. If you have been authorized as an End User of a license, you will have received an email notifying you. Just log in with your MyZemax email address and password. If it says you are not authorized to use the license, see the next section below to find the License Administrator and request access. 

You are not authorized to use this key


This occurs when you are trying to log in and use a subscription license. These license types are indicated by an "Activated" checkbox in the License Manager. To use a subscription license, your Zemax account must be authorized for that license by the License Administrator.

If you get the "not authorized" message you need to request access from the license administrator. To find the administrator, open your Zemax account profile page.

Unable to view License 

This section applies if your computer connects to a server with a network red USB or softkey license for Opticstudio or Lensmechanix, rather than a license installed on your computer. Below is an example of a working license:


Go through each step one at a time. Test OpticStudio in between each one. 

  1. Check your OpticStudio version (displayed when OpticStudio opens). Network licenses require version 15.5 or higher and 16 or higher is recommended.
  2. Check your network connection is active and you are on the same network as the license server. If your computer is connected wirelessly, verify you are connected to the appropriate wireless network. Typically "guest" wireless networks at businesses do not allow access to company servers such as one that hosts your Zemax license. 
  3. Restart the computer. This will also restart the license manager service and often resolves the issue. 
  4. Verify the license server's name is specified in the Sentinel Admin Control Center, see "Configuring Zemax applications to access a Zemax network license".
  5. If you cannot get to the Sentinel Admin Control Center web page linked at the top of Zemax License Manager (or the "Troubleshoot" page in May 2019+ releases), then the licensing runtime is not working. The fastest way to resolve this is to open C:\program Files\zemax opticstudio\opticstudio_prerequisites.exe which will reinstall all licensing and other components needed to run Zemax software. There are also more license runtime repair options in "How to Troubleshoot softkey license issues".

If none of the above resolve your issue, the server may be down or there may be another issue. Check with any coworkers than also use the Zemax network license and see if they can use it or not. You may want to ask the License Administrator of the license as listed in your Zemax account profile page to check on the license server or help further. 

Can see license but get "Cannot find Zemax key" error


If Opticstudio cannot find a valid license, it will first bring you to the License Manager to try and help you find a working license. If you do not choose a valid license, you will get a "Cannot find Zemax key" error. This section helps you identify the cause of this issue when using a network license. This section assumes you have the Zemax License Manager open and on the "View License" or "License Information" page,

  1. Check the number of available license seats. It must be more than 0 to be able to use the license. Check with your coworkers to see if anybody may have left Opticstudio open and no longer needs it. Below is an example of a license with 5 of 5 seats all available for use. 



  1. Check the date of the license. This will let you know if a license is still valid and eligible to run the software. If the license date is Jan 01, 0001, skip to License date is Jan 01, 0001.

Compare the support expiration against the release date at the top of Zemax License Manager. If the Opticstudio release date is newer than the support expiration date, it is not eligible to work with this license. You will need to install an Opticstudio release dated before the support expiration. Check the Opticstudio Downloads page for a compatible release. Note that network licenses are compatible with Opticstudio 16 or higher.  

Example: A valid license with expired support but an ineligible release installed. Note the light red date text in the May 10 2019 Zemax License Manager. 




Example: If a license is expired (invalid), the license will read, "Key expired at," and is surrounded with red (Nov 2018 or earlier releases), or the date is in bold red text (May 2019 or later releases). This means the license was a subscription that was active for a limited time. It is now inactive and is not valid to run any version of the software. Contact your Zemax account representative for help, or try another license if there is one on the list. 





The license date is Jan 01, 0001

If there is this invalid date, or the words "unknown key error" (remotecommerr), This means either there is an issue with the license on the server, or the server administrator has blocked your machine or windows user account from access to the license. Check if other computers or coworkers at your organization can use the same Opticstudio license. If they can, the license itself is working. Contact the administrator of the server that hosts the license at your organization to check if the license is working properly, and that your computer or user account is not blocked from accessing the license. Zemax support does not have this information as Zemax does not host customer licenses. 

Example: A license that the server administrator has blocked you from using it. Note the missing key serial number. In the May 2019 Zemax License Managers you will see the "RemoteCommErr" directly on the View License page instead of the license number. zlm_net_license_blocked.png


Check Out issues

This section covers the most common errors when checking out a license seat on client machines as described in the License Check Out section of "How to configure the keyserver and clients for Zemax network licenses".

Note that the check-out feature is optional - As long as you are connected to the same network as the key server, Opticstudio will find it and launch. If you need to dedicate a seat for use for a period of time or take it offline, you can check out a seat. Use it sparingly and check it in when done so others will have access to the licensed seat. 

The Check Out button is greyed out and unavailable

The section will help if the Check Out button is greyed out and cannot be clicked. 

There are 3 possible causes of this issue:

  1. You are trying to check out a network license seat from the same machine that hosts the license. License checkout only works on client machines, not the license server. If the license type is listed as "Local"  or "Hardware" in the Zemax License Manager, you cannot check out a seat. 



  1. A licensed seat is already checked out on your machine. Look through the list of keys to ensure you do not already have a licensed seat checked out. To do so, look for a license with a line stating Checked out until and a Check-In button similar to the screenshot below. You cannot check out multiple seats at once. You need to check one license seat in before checking out another. 

Tip: If you need to extend the expiration date, you can check-in and check out the same license anytime. Just make sure you are on the same network as the license you checked out from originally. 

  1. If you do not see a checked-out license seat on the list above and it's not listed as "local", then you are trying to check out a license from a server with a Red USB license, which does not support license check out. 

Error: The server administrator has disabled license check out

Contact your organization's IT support. Ask them to enable license check out on the server hosting your Zemax network license. You can get the name of the server from the "Hosted On" line in the Zemax License Manager. Refer them to the "Detachable License" section of this knowledge base article on server configuration: "How Do I Monitor and Control Usage of the Network Key?".



 Error: NoDetachableFeature


This error means there are no seats available to be checked out.

  1.  Make sure you are not already using the last license seat by closing all instances of OpticStudio or Lensmechanix. Launch the Zemax License Manager separately from the Windows Start menu and attempt to check out again.  
  2. Be sure that there is an available seat to check out. See the screenshot below for an example. If there are a total of 2 seats and 0 available, there are none available to check out. If you have verified there is at least 1 seat remaining, but still get this error, the server administrator has reserved some seats so they cannot all be checked out. You will not be able to check out a licensed seat until another person checks one back in. 


Error: License check out could not be completed or RemoteComm error


To correct this error:

  1.  Make sure you are not already using the last license seat by closing all instances of OpticStudio or Lensmechanix, then launch the Zemax License Manager separately from the Windows Start menu in either the Opticstudio or Lensmechanix folder.
  2.  Check that the available number is larger than 0. If there are available seats, and the check-out process still fails, contact the administrator of the server hosting the license. Ask them to restart the "Sentinel LDK License Manager" service on the server, and verify that detachable licenses are enabled. You can refer them to the following article: "How do I monitor and control usage of the Zemax network license?".

Example: No seats available to check out. 


The machine with a checked-out license seat was lost or crashed

Licenses must be returned by the machine that checked them out, and cannot be returned from the server machine. Therefore if a client computer with a checked-out license seat is lost, stolen, crashes, or has Windows reinstalled, that license seat will be unavailable until the specified expiration date. For example, if you check out a license for a 30-day duration, and the client computer is stolen on day 1, you will need to wait 29 days for the expiration.

If you encounter this situation and need a temporary license seat, feel free to contact the Zemax support team. Include your softkey license number (Such as L100000). Note that temporary licenses are available for 30 days or less.


Getting Help

If you are still unable to resolve your license issue, contact Zemax Support.

Please include as many of the following items as you can with your request. 

  • License key number (L1XXXXX) or key id number 
  • A description of the issue you are having and any error messages you received
  • What you have already tried to resolve it

A screenshot of:

  • The Zemax License Manager "License Information" or "View License" page
  • The "Sentinel Keys" page and "Diagnostics" page from the Sentinel Admin Control Center (or let us know if the Admin Control Center page does not work). 
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