I would uninstall the things you installed one at a time as that seems to have caused this.

bitman
I would uninstall the things you installed one at a time as that seems to have caused this.

 
Good idea. I'll do that next. Right now I'm running a full virus scan, which may take a while.

The virus scan didn't reveal anything.
 
I've uninstalled all the IK Multimedia stuff (including Authorization Manager). I've uninstalled Melodyne. Also re-installed Sonar. Re-booted after each stage. Still the runtime error messages persist.

Next I was intending to do an o/s repair from the Windows installation disk, but the Windows disk didn't give me that option. I'm sure it used to be possible in earlier versions of Windows.

I'd never ever done a system restore before, but it seemed like a good idea in this case. I restored the o/s to the point before yesterday's Melodyne installation. Now everything appears to working fine. SUCCESS!
 
Not quite everything though. There has been another intermittent problem all along that I haven't mentioned yet, but I'll start another thread for that.

From now on I'll be installing items one at at time and checking that each one works before continuing. So if I need to backtrack again, it won't be too far back. And I'll be giving Melodyne a miss.