Movie Studio Platinum 12 had been working well on Windows 10 for about a year but a recent update of Windows has caused chaos. The symptoms were an error message (Microsoft Sound Mapper missing) followed by crash of Movie Studio - the update also blocked internet access. So, after various failed attempts to cure the problems, I tried running Movie Studio in compatibility mode for Windows 7 - as far as I can see, this has solved everything.
Unfortunately I can't tell which update caused my problem because I had been away from home for 6 weeks, so there was a large backlog of updates for my desktop computer when I returned - one of them was the culprit!