Diagnosis
You cannot reverse the material documents which you selected becausethere are already follow-up documents for them. If you do not reversethe follow-up documents as well, the quantity posted will be negative.
Example:
1st material document: goods receipt; BWART 101; 8 pieces
2nd material document: quantity reversal; BWART 102; 2 pieces
3rd material document: document reversal for document 1; BWART 102; 8pieces
The total of the quantity posted would be -2, that is the vendor wouldhave delivered a negative quantity.

Procedure
You have the following options:
First carry out a document reversal for the second material documentwith the quantity reversal, and then a document reversal for the firstmaterial document.
Carry out a document reversal for the first and the second materialdocument at the same time.