Diagnosis
You are attempting to change the assignment of a reference material toa material group. This is not possible in this case as other materialgroups are also assigned to this reference material.
Moreover, this reference material is assigned the material group forwhich you wish to delete the assignment in its material master. Thismeans that the deletion flag you are requesting cannot be set.

System Response
The system cannot carry out the change.

Procedure
First change all other existing assignments; then you can change theassignment to this material group.