SAP Message >0028 - Formal error: Installment plan allows only one partner and one contr.acct

Diagnosis
Program error during creation of installment plans. You must ensurethat the same business partner and contract account is entered in allinstallment plan items. This condition has not been fulfilled in thisparticular document.

System Response
Error message. Processing is terminated.

Procedure
INCLUDE NA_SYSADMIN1 OBJECT DOKU ID TX

Procedure for System Administration
INCLUDE FICA_NA_OSS OBJECT DOKU ID TX