SAP Message VFRR533 - Subsequent documents mean that you cannot change the revenue recog. cat.

Diagnosis
You cannot change the revenue recognition category if:
Revenue has already been recognised
The document has already been billed

System Response
You cannot change the revenue recognition category.

Procedure
You can only change the revenue recognition category in Customizing forthe item category. Re-enter the original revenue recognition categoryfor the relevant item category.