Scheduling terminated: Check lot size unit of measure

What causes this issue?

The lot size cannot be converted into the routing's unit of measure.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

INCLUDE 'NA_ALLG_URSACHEN' OBJECT DOKU ID TX
RESET N1
Check the unit of measure that you have maintained in the routing.
Change it if necessary.
Check the conversion factors specified in the material master. Change
them if necessary.

Error message extract from SAP system. Copyright SAP SE.