You cannot delete the last row

What causes this issue?

Every restriction group must be assigned to at least one planning
version.

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?

If you want to delete this connection, proceed as follows:
Create a new planning version.
Link the restriction group with this new planning version.
Delete the desired connection.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.