Hi Karl,
That kind of problem can show up if the aircraft's compiled code used an older SDK. Since this problem doesn't show up for anybody else (assume you checked that), you need to make sure that you are using the latest version of A2A's aircraft for P3Dv5.1 HF1.
Have you redownloaded the correct A2A package from A2A to make sure the version you are using is the proper version?
Other than that, not sure what could be causing it.
Rod