System Crash during VATSIM long haul flight

Hello,I'm a new user of PMDG744.I tried to make a flight from KLAX-RKSI(South Korea) using the North Pacific route.However, the system crashes between 5~7 hours when I pass the Alaska and enter the Russian airspace on G212.When I tried this flight without SquawkBox, i could make the trip, however, with Sqkbox the same crash occured.Using the newest FSUIPC 3.71.