What tool are you using to connect to your universes, Webi, Deski or?
Usually this happens due to the wrong date format being fired at the database. In Business Objects PRM files control the INPUT_DATE_FORMAT.
The file you are looking for is the oracle.prm.
Where you change this depends on the tool being used, obviously if it is Webi you have to change on the BO server, if it is Deski you have to change the workstation.