erore

i get and error message every time i try and open medieval it normally says

colume_building_faction_association
unknown faction specified:column 20 row 9
fn_byzantine

any help would be appreciated

Did you mod you game? If so, it's an error within the unidproduction files. Go to your main folder were your .exe is located, thier should be some notepad files. One of them is called CRUSADERS_UNIT_PROD11. Open this file with Gnome, which you can get from the dowloads section at the .org. Check line 20, and look under your "faction advatages". You should find an incorrectly marked "FN_BYZANTINE".

OR

Your may have installed a mod that only works for MTW:VI, if you have vanilla only that is...