Thanks for your advice!
Will start the Software in Debug-Mode the next time.
Had the Problem again a few minutes ago, and there was no Problem with “LBFileDialog.exe”, so i think it was a coincidence…
But i agree, it could be a File Locking Problem when Lightburn tries to save a File, while VSS takes the Snapshot for Sync.
Have to walk the Dog now, so more to come the next days… 
Thanks a lot for your Support! I appreciate this a lot!