Note: There might also be a simple mistake such as an error in a line of the DLL file. Example: Instead of having "Air Nav", you read "Air Mav".
Still having issues:
If you notice a mistake in the file name given on the FSX error message, for example reading "AirmavBridgeFSX...", with an "m" instead of an "n", you should try doing the following:
Rename ALL the files related to the FSX Air Nav Pro plugin with the same mistake (put an "m" and remove the "n").
For example: if you have AirnavBridgeFSX.dll, rename the file to AirmavBridgeFSX.dll