I have the same issue - it's a real pain. Everything was fine until a few weeks ago.
For me, this happens when I try to export a song - during the export, the progress bar stops (it never used to) until it's about to complete.
After completion, one VSL sample set displays this error and the only option is to replace it with a different vst and then replace it with the correct one. If I save the song and reopen it without resetting that VST, the reopened song doesn't work properly.