Are you installing as Admin? Try that first.

 Otherwise, it sounds like either your security software or UAC is blocking it. Try turning these off while installing.

Specifically, run the program as admin, not the installer.  The issue is that the folder it's trying to write the activation signature file to isn't allowing the file write operation due to permissions issues.  Running the program as admin allows that to happen, as the program is calling the activation, not the installer.