Tables locked by user &1.

What causes this issue?

You attempted to edit a root node in the change mode.
Someone else is currently editing this root node.

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?

Wait until the other user completes editing and releases the block.

Procedure for System Administrators

The key root directory is locked in table SHDFOLTREE.
If necessary, this lock entry can be removed with transaction SM12.

Error message extract from SAP system. Copyright SAP SE.