Hello,
I have the same problem, i have read that on Facebook "There's a fix someone posted on pmdg 777 forum on avsim. If you use fsuipc, delete fsuipc.ini then start fsx, it rebuilds automatically a new one .ini (that solves the problem for the users having this trouble)" But i can't test now because i'm in flight.Try this if you want, it can help you.