I have bought digital camera sony s500 and MS pro duo but it can't fit,it's too long.What is the problem?

what's the too long????....the memory stick pro duo((which should be shorter than the pro ))???? or ...the slot is too long ?????....i think u meant the slot.....!!!
anyway ...ur camera support the memory stick pro ((the longer )) up to 4 GB...the memory stick pro due is not supported.
return it back and get the the pro((longer and cheaper)) or get a Memory Stick Duo Adapter to put ur memory stick in and use it in the camera.