Please Help ATC Issues

Ok so I am flying in a KAL PMDG 777-300er from KJFK to RKSI and I loaded a flight plan from flightplanner.org into both the FMC and FSX flight planner. Whenever I ask the ATC to increase or decrease my cruise altitude, the options go blank and I can't respond or do anything on the interface. I have never had this problem before with PMDG and other aircraft and I dont know whats causing it. It was working absolutely fine on my inbound flight. 

ALSO: I tried creating the fplan inside fsx using the default flight planner and the same thing happened. I can do everything else accept altitude change.