SAP Note 16236 - Create material: error in ext. number assignment

Symptom:

When you create a material (MM01) with a purely numerical external number, the system issues error message M3565:
External mat.no. may not consist solely of digits with this material type".

Cause and prerequisites

Check for external number assignment has been deactivated.

Solution
Use OMS2 to remove the indicator for not(!) checking the external material type for the material type involved.