Article hierarchy & is blocked by user &

What causes this issue?

The material hierarchy is blocked by a user who is creating the
hierarchy with the same hierarchy ID.

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?

Ask the user who set the block to release it again.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.