After upgrading to Trados Studio 2021 SR2 CU10 - 16.2.10.9305, you receive the error message below when opening Trados Studio:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<sentinelInfo><status><statusCode>210005</statusCode><statusMessage>Cannot talk to the license server on host "xxx".
Server not running?</statusMessage></status> </sentinelInfo> 



The main error may also be: 

Service 'Sdl.TranslationStudio.Api.ProjectManagement.IProjectManagementService' could not be started.



An error occurred while requesting a license. Click Retry to try again.

Install the new LicenseServerManager18.0.79 on the server\computer where the network license is activated, instead of the older versions, License Server Manager 16.2.496 or SDLLicenseServerManager_2.0.27550, which are no longer compatible with Trados Studio 2021 SR2 CU10 - 16.2.10.9305.
 
There is no need to uninstall the old version of the License Server Manager or deactivate the licenses prior to installing the new version. Simply double-click on the installer, once downloaded from your RWS Account, under Products & Plans > Downloads > LicenseServerManager18.0.79, or the direct link below and it will overwrite the old version.

https://downloadcentercdn.sdl.com/TP/Trados/T2024/Licensing/RTM/LicenseServerManager18.0.79.exe

Note: The new version of License Manager is compatible with older version of Trados Studio / Passolo. 

Trados Studio 2021 SR2 CU10 - 16.2.10.9305 and newer is not compatible with License Server Manager 16.2.496 or SDLLicenseServerManager_2.0.27550.