How to delete old Trusting-connections

Hello,

I would like to create a new Trusting Relationship in SMT1 while an old one for the System doesn't work.

Before I can do that, I must delete the old Connection in SMT1. After selected the System and press the Delete-Button

got the following message:

I've checked all rights, and change to SAP_ALL/SAP_NEW, but cannot delete the old Connection. Is there a Special Table or security mechanism where the old Systems are stored and could be delete? So please help me. Thank's