Same item is selected for predecessors and successors error is thrown even though there is no same items selected. This occurs when capabilities visibility is OFF on menu items.
- Make sure Enable Capabilities is OFF in Administration > Platform > Solution tab
- Navigate to work items like Features/Epics
- Open a work item and go to Links tab.
- You can leave the selections blank and click View the Predecessors and Successors button
It should open the define links view
Enable Capabilities in Administration > Platform > Solution tab.