EXS 24 Logic Sampler Users Group

I have just encountered a new proble mthat is driving me nuts.
I have been working on 4 mixes of atrack all week and have got them done
nicely. problem is that the sax tracks i have layed over my finished mix go
out of time every time I bounce it down. I have tried everything. The same
thing happened to my vocal mix. Main track done and dusted. put the vocal
pieces down and again every time i bounce the whole thing goes out of time.
This has never happened to me before in 5 years of using Logic.
Please someone help! I need to get this project on to CD and start on
something new.
Cheers 
Lee