IDoc & could not be processed

What causes this issue?

The IDoc contains more than one article (segment type E1MATNR).
For each IDoc you can only process one segment of type E1MATNR.

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?

Create only IDocs with one article (segment type E1MATNR) and the
corresponding listing conditions.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.