"Program Error" message in the FMC?

In an effort to learn about the route between Boeing Field (KBFI) and Moses Lake (W20) I created a Flight Plan in FS Navigator before exporting it to the Cargo 747.When trying to enter KBFIW20001 into the Co. Route line I receive a message reading "Program Error".I've tried creating another Flight Plan ending in 002 but with the same result.Is there a way to solve this problem please?Cliff