Multiple downstream nodes are connected to the listed node and at least

What causes this issue?

one of those nodes is not a mp type 17 (allocation), 04 (deduct), 12
(theoretical), 54 (glg receipt), 57 (rlf receipt), or 56 (injection
meter).

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.