Error message in Trados Studio when checking in file from a Trados GroupShare project: The process cannot access the file because it is being used by another process.

When trying to check back in a file from a Trados GroupShare server project, instead of the file being returned to the server the following message appears: 
The process cannot access the file "[...PATH...].sdlxliff" because it is being used by another process.

To solve the issue please follow below steps:

1. Remove the server project from your Trados Studio list of projects: go to Projects view > right click on the project where the issue is happening > select Remove from list
2. Open again the server project to a different folder than the one where you initially opened it
3. Check out again the file that you worked on and use Pre-Translate (assuming that you used a Translation Memory) to recover your translation on that file
4. Now you can check the file back in to the server.

NOTE: In some cases the corruption appears on the server side (Application Service locks the file) and even if the project is removed and the file is downloaded again the error message still appears. Unfortunately we do not know the root cause for this issue at this time but the workaround is to upload again the file to the project (Add new file) and use pre-translation if a TM was used.

It may be that the sync between the local project and the server project is no longer working correctly.