The reason is probably the user account control in Windows Vista. Turn off the User Account Control to get the full rights
How to turn off:
After deactivation make a new start of your pc. Now make your (hopefully last) online activation.
Also when running the game itself especially when first registering you should run it as Administrator, just being logged in on an Administrator account is not good enough.
You either need to right click on the games start Icon and select, "Run as Administrator" each time or set this in the Games start Icon by selecting Properties then choosing the Compatibility Tab and then at the bottom check marking the "Run the program as an administrator" in the Privilege Level box.