(mods this is about the .dll file and not payware)
I installed the PMDG 747X but when I came to fly it I was told that the PMDGOptions.dll couldn't be found.
The PMDG site has a good wiki based knowledge and support area, and I discovered this was not an uncommon problem.
I uninstalled the 747, the Level D 763 and FSUIPC all of which use the .dll file - which resides inside your Roaming folder, then inside the Microsoft folder and inside the FSX folder.