Windows 7:
I recently re-installed my FS 2004 directly onto my C drive to avoid the annoying; "permission" problems....
..but my FSX (and IS3, etc) is installed in the default "Program Files"....

...., and gives me no problems, providing that if I decide to change a file, etc, I drag it onto the desktop, change it, and then drag it back to its original location again.....the disadvantage of using "Program Files"!
It generally appears to be better to install our Flight Sim programs in a different location to "Program Files" to avoid ongoing problems!
If I can remember, there were no such problems with the lovely-old Windows XP..

....!
Paul...A Permissions Rebel!...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.