I changed the drive letter and everything seems to be working perfectly. No problems with plug-ins or plug settings whatsoever, and I have plenty of plugs in each project so I'm sure I would have triggered an error by now if there was going to be one.
I've seen CLSID errors before from Sonar plugs but all you have to do is remove the existing plug and insert the new or correct version.
I'll continue opening projects for a while, until I'm absolutely sure but this has to happen so if I have to fix the occasional error so be it. It looks as though it's going to work perfectly.