which is exactly the same issue as I'm seeing, but that thread has been marked as resolved. I used the tool mentioned in that thread to see what process is using it, and it looks like explorer.exe is the culprit. Any ideas on what might be causing this? I've had this same message on a few files today. Also worth noting, I'm trying to checkout the drawing, not the part, but cannot check out the drawing because the part is being used by explorer.exe. please see screen shots.