An IDoc without a message type was passed to the ALE layer

What causes this issue?

The IDoc passed to the ALE layer could not be processed. The settings
in the control record were not correct.
The logical message type (field MESTYP) was not passed.
The attempt to copy the value of the EDI message type (STDMES field)
also failed, because this field was also empty.

How to fix this error?

The fields mentioned above did not contain the values which they should
have done in the calling program.
Make a note of the transaction in which the error occurred and inform
your ALE administrator.

Error message extract from SAP system. Copyright SAP SE.