Cannot delete delivery phases for &1 &2 &3

What causes this issue?

You tried to delete a delivery phase for a particular material-store
combination. However, either an allocation table has already been
generated for the material or it was blocked in the promotion.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.