Saved Flight Problem

I'm usually pretty good about troubleshooting FS, but this one has me stumped. When I load an enroute saved flight, the sim will freeze for several minutes, but the sound is running. I can only exit after it finally "loads", but am treated to the same problem if I switch views. And this doesn't seem to be consistent, sometimes a saved flight will load fine, especially if I start on the ground. Happens to different aircraft as well. Anyone have a similar experience?Thanks