Well I am at an utter loss to explain this, but SonicStage is working again. Joy !!!
All I did was boot into safe mode and try running SonicStage. The first time I tried I got the expected error message saying the application had stopped working, but with a weirdly optimistic sense of persevenence I decided to try again, and this time it worked! SonicStage started up, no error messages were displayed and I was able to access the menus, etc. This was all on a blank database, so I shut SS down again, copied across the backup of my database and restarted; and SS still worked. All my artist & album details loaded correctly, I could change views and sort lists; basically everything seemed to be running fine...touch wood.
So to confirm that this wasn't just a fluke, or would only work in safe mode, I restarted Windows and openned SS again - still working!!! Sooooooo Happy
I have no idea what may have changed for SS to suddenly start working again, and frankly, as long as it continues to work, I don't really care.
Just thought I'd update on the status of this on the off chance it may help someone else.