"Could not access network location %APPDATA%" install errors

Symptoms

While upgrading, installing or uninstalling a Windows software package (such as iTunes for Windows or QuickTime for Windows), you may receive the following error message:

Could not access network location %APPDATA%

Resolutions

This is a 1606 error message (even though installers for Apple-created Windows software packages typically do not return the 1606 error message number with the message).

So, first try the automated Fixit from the following document:

You receive an "Error 1606" error message when you try to install or remove a Microsoft program

If the problem persists, next try the automated Fixit from the following document (which should be effective against a different class of causes for 1606 errors):

Fix problems with programs that can't be installed or uninstalled