In case anyone stumbles upon this. I did manage to get the remove command to work after restarting the StarWind services.

Then running the DPM command worked with no issues, and then I was able to add those virtual tapes back to open locations.

We've been running MS DPM and VTL Free for a while now with no problems. After this weekend I noticed that in the Tape Library section of DPM I was no longer seeing the 4 Tape Drives from the Library, but I could see all of the tapes. I found some resources that advised shutting down the DPM service...