This is a known issue with 2009LT PreUpdates. What updates have you applied?
I would start with Autodesks Update 1 which can be found here http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=11581572&linkID=9240618
and then update 2 which can be found here http://images.autodesk.com/adsk/files/autocad_2009_and_autocad_lt_2009_update_2.html
You can read more about the features and fixes here http://heidihewett.blogs.com/my_weblog/autocad_2009/