The last delta load is still running; no new request possible

What causes this issue?

The last delta load is still running; no new requests possible.
A repeat request is currently running for this DataSource.
You can only request a new delta once this loading process is
completed.

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?

Check the status of this delta request in the Monitor.
If the load has been terminated for some reason, remove the error;
Set the request to red or green using QM action, so that the next delta
or repeat can be requested.

Error message extract from SAP system. Copyright SAP SE.