Some 3rd party a/c freeze MSFS2002 when in SB

I have a PANAM and QANTAS B707 and the highly ratd AMERICAN AIRLINES B727 ADVANCED (in MS FS2002 PRO and WINDOWS XP) - if I try to use these aircraft with Squawk Box and Roger Wilco they crash out the sim either immediately or just out of the blue after a couple of minutes running. Most of the other aircraft (both default and 3rd party) seem to work just fine.Wondered if anyone else has experienced this or had a work around, as these aircraft are real favourites to fly.