Cannot upgrade WPI 3.0

When I try to upgrate my copy of WPI 3.0 I get a "The feature you are trying to use in on a network resource that is unavailable" message looking for "wpi.msi".

The only version of this file on my harddrive is in [User]\AppData\Local\Temp, but it won't accept that file.

When I click cancel I get the error message "The older version of Microsoft Web Platform Installer 3.0 cannot be removed. Contact your technical support group"

I've googled this of course, but I couldn't find any hits for WPI 3.0.

Trying to remove the older version from Control Panel results in the same prompt for wpi.msi. Is there a registry key I can remove to prevent the uninstall?

Thanks