Ah then it sounds like you have a corrupted game file; move all your downloads out and try, this will eliminate a conflicting download or mod. If that solves it - find any recently downloaded mod and remove it.
if not - then is most likely a corrupted objects.package file.
see this article at MTS2 for instructions on how to extract and replace the objects package file:
http://www.modthesims2.com/article.php?t=134921