Do you have the latest version of FSUIPC installed?
Also try the following....
1. Right-click on the PFE shortcut and select Properties
2. On the tab labelled Shortcut, click on the button labelled Advanced
3. Tick box labelled Run as administrator and then click on the OK button.
4. When prompted by the system, click ok to confirm.
5. Select tab labelled Compatibility
6. Tick the box next to run this program as administrator then click on the button labelled Apply
7. Finally, I click on OK to exit.
Other important things we always tells users when installing on Vista and/or Win 7:-
(a) Turn UAC off.
(b) Log on with Admin rights
(c) NEVER install into the Program Files folder because the OS will prevent some files being updated
(d) Stop all other programs during the installation, especially virus checkers and any other security type programs