Check the folder C:\Users\Yourname\AppData\Roaming\Microsoft\FSX.

Note Yourname will be your actual name.
The fsx.cfg folder will be found by opening FSX.Open it with notepad and look for the [Trusted] section.
It may be quite large.Delete all  the relevant entries,e.g. for the 707, and save it ,then reinstall the 707.The FSX program should then rebuild your fsx.cfg file.Hope this helps.
Ron