Error in 'PART_OF'/'SUBPART_OF' dependency

What causes this issue?

The syntax check found an error in the entry for predefined standard
dependency <ZH>PART_OF</> or <ZH>SUBPART_OF</>.

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 your entry and correct the error if required. See also other
possible causes of error (messages).

Error message extract from SAP system. Copyright SAP SE.