In order to perform some tests on cross-trackers triggers, I first created a 'Tests' tracker and I've set the built-in 'Tasks' tracker to be a child of the 'Tests' tracker. The parent 'Tests' tracker had a 'Status' field, and the children 'Tasks' tracker initially had two drop-down boxes, respectively labelled 'First select box' and 'Second select box'. I also defined a cross-trackers trigger so that when both drop-down boxes in every child task are set to 'Done', then the status of the parent 'Tests' tracker is set to 'Done'. This worked fine, alright.

Then I decided that, for this tests, one drop-down box would be enough in the child 'Tasks' tracker, so I renamed 'First select box' to 'Unique select box' and I deleted 'Second select box'. But I hadn't changed or suppressed the cross-trackers trigger before doing this, and when I came back to the triggers definition/modification tab, in the 'Manage Workflow' administration screen, I got a fatal error (see attached screenshot) and was unable either to submit or cancel any modification in that triggers definition/modification tab.