fsx-ms 3rd party install

[CV21 0]

Running Win 8.1 64bit, Geforce 630GT/2gig, 3.0 Intel i5 4430 with 8gigs of ram, Lenovo K-450 desktop. Had to do some repairs and when everything was ready to go FSX was operating but most of my 3rd party addons have texture problems.  For the moment my main concern is my Cheyenne payware.  It always showed up all black.  I finally uninstalled and tried to reinstall using the disks for the aircraft.  I get as far as selecting the aircraft install, asks for ID number, accepts that, then shows location C:\FSX, (which is where I have my FSX installed) I click OK and then I get an error (appdata) access denied

I run everything as adminstrator.  Under folders permissions are granted to myself and administrators.  I've made several attempts, I have rebooted the computer and have exhausted my limited knowledge of FSX.  I hate to bother people but I sure could use some help.  It will be appreciated..