HI ,
Its really strange FBU8 doesn't allow to reverse any document which is not cross company code . FBU8 is only to reverse the single document. Individual company code document should be reversed by FB08 . FBU8 transaction has push buttom for mass reversal which takes you to F.80 Once you are on F.80 you can reverse the individual company transaction as well Cross company code by choosing the cross-company code tab . If you do not want to process the Cross company code transaction please choose " do not process " .
Please see below screens shots.