Can you suggest How to and where to check master maintained for this 'A4'. Anything is misssing in master or not ?
In MM02 under sales :sales org2, see below.
similary for customer master in Xd02->under sales area data tab->billing documents -> you can see acct assgmt group here you check.
if you maintain the correct account groups (which are having GL accoutns assingned)in the above both master system will not thprough any error in future.
And for current document you can goto VF02-goto->header-acct Assg GR and also at item level with the sames path if you correct the correct AAG then the current error can be overcome.
thanks,
Srinu.