Have you run as administrator?

I believe Impulse is respectful of the original OS environment into which it was originally installed. When I installed Impulse for example, I had my McAfee VirusScan On-Access Scan enabled at the time... if I turn it off, which I always do before I game, Impulse comes back with precisely that same error.

If I re-enable it, Impulse runs no problem.

There are many antivirus packages that monitor MyDocuments and don't allow writes to those files. I would disable the software for install then go into the settings once Impulse is installed to allow for the service to be running. Please note this can sometimes apply to SpyWare as well so better safe than sorry.

I am the admin and anti-virus is turned off.

Try running this:

http://sd.stardock.com/mike/apps/stardock_access.bat

This should fix any permissions issues for any Stardock apps.