Diagnosis
You have assigned a flow type to a condition type with the propertyAdvance Payment. The Revenue indicator is set for thisflow type, and it is designated as a special G/L transaction. However,when the system posts flow types (in particular for determining taxaccounts), it assumes that only those 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, deselect the Revenue indicator for thecorresponding condition type.
If the advance payment is to be posted as revenue, deselect theSpecial G/L Transaction indicator in theaccount determination.