Hi,
what BO version do you use? There is a bug in BO 6.5.2 that causes the report originally saved in BO 6.5.2 and then open and saved in 6.5.1 to become very large.
Have a look also at these post: here and here
Hope this helps.
Marek Chladny 
(BOB member since 2003-11-27)