In Tcode : ME22N- While changing PO-Error is raising .

In the transaction code : ME22N- While changing Purchase Order, we are getting the following error message :

ENTER VENDOR DETAILS BEFORE PAYMENT TERMS.

1. We are got this error only rare cases(up to now only one time).

2. I have checked in Message Classes(MM), Text elements and in program, but i have failed to find where it is and from where it is raising.

Can you please send me the solution & path from where it is raised.

Thanks & Regards,

Rafiq Gajula,

Mail: Rafiq.Gajula@lntinfotech.com.