It is possible to post the same Document No. multiple times in the Cash Receipt Journals area. However, in order to reverse the entry, you must choose a particular Entry No. and click reverse. This only reverses at the Transaction-level, though, so if you have posted portions of a document multiple times, you have to find an Entry No. from each specific posting and reverse them individually. Moreover, there's no report that shows all of the Transaction and Entry numbers associated with a Document Number, so identifying the correct Entry No. to reverse can be pretty difficult.