I recently experienced a new (at least to me) FSX issue which Pete has asked me to document here. The problem was found when an updated version of FSUIPC wouldn't load into FSX even though the older one was loading fine, however the problem is actually generic and could affect any module.   There is a Windows registry setting which will result in FSX automatically mistrusting new (or updated) DLLs, without prompting. If you have a DLL that just will not load, and you do not even get prompted w