HI Kali Li,
Technically SAP allows you to assign multiple successor relationship with same activity. This should not be allowed. You should raise this to SAP to make correction.
Meanwhile you can achieve your requirement by using user exits in validation rules where following needs to be configured:
1. Prerequisites: if the user statuses (like open, PO creation etc.) has been set.
2. check: Z user exit, in the activity tab for a particular activity, multiple checks boxes (AFABD-NCHKZ) should not be active for combination ACTIVITY-NETWORK.
This validation will not allow user to save network activity if multiple relationship exists with same successor activity.
Thanks and regards,
Narender.
