Aha! My HKEY_CLASSES_ROOT\CLSID{B54F3741-5B07-11cf-A4B0-00AA004A55E8}\InprocServer32 (Default) had a leftover dll from recently-uninstalled Avast virus scanner.
As admin, changed HKEY_CLASSES_ROOT\CLSID{B54F3741-5B07-11cf-A4B0-00AA004A55E8}\InprocServer32 permissions to allow updating, then replaced the (Default) value with
C:\Windows\system32\vbscript.dll
I had the same problem, and I had uninstalled McAfee before. Taking ownership of
HKEY_CLASSES_ROOT\CLSID{B54F3741-5B07-11cf-A4B0-00AA004A55E8}
and then changing the InprocServer32 value to point to C:\Windows\Systerm32\vbscript.dll fixed the problem.
Note this was on a brand new Dell notebook computer that came with a 30-day version of McAfee installed. I have even more reason to hate McAfee now.