Account requires CO account assignment object

Hi Experts,

While we doing PGI the system is giving the above error in PRD system and we activated the CO PA module and we defined the same as a cost element and assgined in OBYC/GBB/VAX,VAY also.

And the account 321000 is an COGS account and infact till yesterday there is no problem with this but from today morning if we do any GI we are getting the above error and also we didnt assign anyhting in OKBY but still working fine till yesterday for all materials in all plants.