Diagnosis
V3 was defined as company code group for contract account v1.However, company code &V2& does not belong to group &V3&.

Note
When you post a document, an open item is assigned to a company code anda contract account. A company code group is defined in each contractaccount. This company code group defines the company codes that can beused for posting to this contract account.

Procedure
Either correct the company code entered or select a different contractaccount or a different business partner.