Last week I had to restore a VM, and all restore point were not working for this VM.
In the restore tab, for this VM, the "Last Known Path" was "Not Available"...
Any idea what happened, and how can this be prevented?
Not sure how it happened, but it can be prevented by not using VDP in the first place. It's been end-of-life for some time, so you're far better off going with something else out there.
