Re-install (after uninstalling, or deleting warband) just because you might have (more than likely) messed up the core files.
Else, download an OSP package until you properly re-install the game.
Just reinstall right now and back up the native folder, it will save you alot of trouble
http://download.taleworlds.com/mb_warband_setup_1143.exe
native mod comp.
http://forums.taleworlds.com/index.php/topic,126993.0.html
File Listing: Diplomacy - With OSP Items V2
http://www.mbrepository.com/file.php?id=2144