Hs anyone run into this one?

Whenever I try to install a program, I get about 2/3 of the way thru
the installation, and then it stops and I get a message box that says:
"Error 1500; Another installation is in progress. You must complete
that installaation before continuing this one."

I've looked at everything in my Startup folder, run AV software, and
I've tried installing immediately after bootup, I'e also reinstalled
Windows Installer.

Windows Task Mgr. says that nothing else is running.

Any thoughts?