To the op you havnt  installed   the accel pack and than installed sp1 by any chance.

Hello again Bob Sir,

If you are still having probs with fsx/sp1, as a cure all, may i suggest that you indulge in a copy of acceleration- which is the sp1 and sp2 plus with soime little bits and bobs added, all in one simple dvd expansion set. Hopefully this should cure your install ills.  ( These little probs can be frustrating in the extreme sometimes. )