Quota arr. for material & and plant & already being processed

What causes this issue?

The quota arrangement is already being processed by another user.

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?

Try processing the quota arrangement later on.
INCLUDE NA_SYSADMIN LANGUAGE EN

Error message extract from SAP system. Copyright SAP SE.