Close the error message and follow these steps:

1. Go to (you can copy/paste this path in File Explorer in Windows OS):
- for Trados Studio 2022: C:\Users\%USERNAME%\AppData\Roaming\Trados\Trados Studio\17
- for Trados Studio 2021: C:\Users\%USERNAME%\AppData\Roaming\SDL\SDL Trados Studio \16
- for Trados Studio 2019: C:\Users\%USERNAME%\AppData\Roaming\SDL\SDL Trados Studio\15
- for Trados Studio 2017: C:\Users\%USERNAME%\AppData\Roaming\SDL\SDL Trados Studio\14

2. Rename the Plugins folder (for example into Plugins_old)
3. Run a Trados Studio repair (see Repairing your installation of Trados Studio) from Control Panel\Programs\Programs and Features (optional)
4. Restart Trados Studio

If the issue persists, please also go to:

  Trados Studio 2022: C:\Users\%USERNAME%\AppData\Local\Trados\Trados Studio\ and rename 17 folder to 17_old
  Trados Studio 2021: C:\Users\%USERNAME%\AppData\Local\SDL\SDL Trados Studio \ and rename 16 folder to 16_old

or go to
- for Trados Studio 2022:  C:\ProgramData\Trados\Trados Studio\17
- for Trados Studio 2021:  C:\ProgramData\SDL\SDL Trados Studio\16 
- for Trados Studio 2019:  C:\ProgramData\SDL\SDL Trados Studio\15
- for Trados Studio 2017:  C:\ProgramData\SDL\SDL Trados Studio\14 

and rename the Plugins folder (for example into Plugins_old)

Note: If the issue is happening at a Language Office, the plugin is added by the System Admin to the Program Data location and the user is getting this message because the user is trying to install the Language Weaver plugin again. Make sure you check if the plugin is already added in ProgramData and check if it is working in Trados Studio.