Solution : https://service.sap.com/sap/support/notes/98879 (SAP Service marketplace login required)
Key words : 
additional key words co13, process incorrect goods movements, automatic goods receipt, error message m7021, background job coruafw0, program error occurs, program error, program coruafw0, incorrect quantity, program errorrelease 3
Related Notes : 
       
| 198460 | Cancelltn of auto.GR retrns incor. offsettng postn | 
| 86977 | Data inconsistency when canclng GR usng Note 84175 | 
| 84175 | Problems for reversal of a confir. w. goods move. |