Not all documents could be blocked (see long text)

What causes this issue?

One or more documents are blocked 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?

You can execute the program run if you deselect the <LS>Block all
documents</> indicator. Then, documents are not blocked together, but
individually during processing. However, documents which cannot be
blocked are excluded from processing (error message).

Error message extract from SAP system. Copyright SAP SE.