Before installing the Trados Studio 2021 SR2 version, users should clean up the Plugins folder in order to avoid errors caused by the incompatibility between old plug-ins and latest version of Trados Studio 2021. 

1. Close Trados Studio 2021 SR1 CU8 or any older version you are working on now.

2. Go to C:\Users\%username%\AppData\Roaming\SDL\SDL Trados Studio\16 
or paste %appdata%\SDL\SDL Trados Studio\16 in Windows File Explorer and press Enter

3. Rename the Plugins folder to Plugins_OLD

4. Install Trados Studio 2021 SR2

5. Reinstall the plug-ins you were using from the RWS AppStore - the latest compatible versions should be available for installation through Trados Studio, or for download from the website.