Schedule line category & is not defined

What causes this issue?

This <GL:schedule_line_category>schedule line category</> &V1& is not
allowed in combination with the <GL:item_category>item category</> and
the <GL:MRP_type>MRP type</> for this material.
INCLUDE 'NA_NO_PROCESSING_1' OBJECT DOKU ID TX LANGUAGE E
INCLUDE 'NA_CHECK_ENTRY' OBJECT DOKU ID TX LANGUAGE E
You can display the possible entries which have been defined.
To do this, place the cursor on the <LS>schedule line category</> field
and select F4=Possible entries.
Furthermore, you can display the combinations defined in table TVEPZ
which controls schedule line category determination. You can make
changes here as required if you have the authorization to do so. The
MRP type for the material can be changed in the material master.

Error message extract from SAP system. Copyright SAP SE.