Diagnosis
You have assigned a flow type to a condition type with the property Advance Payment, but this flow type is not posted as a special G/Ltransaction. However, when the system posts, it assumes (in particularfor determining tax accounts) that advance payments that are notidentified as revenue are posted with the special G/L transactionindicator.
The current setting causes an error during posting.

Procedure
Decide whether the advance payment is to be posted as a special G/Ltransaction or as revenue. If the advance payment is to be posted as aspecial G/L transaction, set the Special G/L Transactionindicator in the account determination forthe flow type. If the advance payment is to be posted as revenue, setthe Revenue indicator for thecondition type.