Error in tree structure in TBRF230 - Node could not be added

What causes this issue?

Table TBRF230 contains (group) nodes that cannot be included in the
tree.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

There are three possible reasons for the error:
A node has declared itself to be a higher node.
Several nodes have indicated another node to be the higher node and
vice-versa. This isolated subtree cannot be included in the existing
tree.
A higher node has been deleted in the meantime.

System Response

The tree cannot be set up.

How to fix this error?

Adjust table TBRF230 in maintenance view M_TBRF230.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.