No materials found for physical inventory

What causes this issue?

There are two possible reasons for this message:
No materials were found under the search criteria entered.
The system found materials, but these materials are currently taking
part in an active physical inventory.

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?

INCLUDE NA_EINGABE_PRUEFEN

Error message extract from SAP system. Copyright SAP SE.