I recently found a good use for Process Monitor which I hadn’t thought of before:

If you ever have problems with software not working and you suspect it may be a permissions issue, run Process Monitor while the software is running and look for any ACCESS DENIED messages in the Result column. It’s much easier than guessing the permissions you need to set.

Note: Process Monitor is an enhanced replacement for Filemon and Regmon but Filemon would still do the job.