When you reversal billing document by VF11, the error message appeared as below:
Due to this billing which create without refer to actually sales document or delivery document, the may be created by POS or IDoc with Billing category as “W” (filed: TVFK-FKTYP and VBRK-FKTYP); In this case, we can’t revesal billing use VF11 by normal program. We should assign copying requirment route 410 to filed TVFK-GRBED within Billing document. Then we can reversal billing by VF11.
PS: for more detial information, pls refer to sap note 489676, this note just for you reference to resolve issue quickly.