I never worked on a T1000, but it sounds similar to a DMAX shelf. On the DMAX, there was selector switch on the backplane where you had to set the shelf number. Maybe something changed there? What if you remove the protect unit and just run on one working unit, any change (or vice versa)? I know I had an issue one time where I had failed communication between shelves, and found out someone had bent the pins on the back plane when trying to insert a new service card. Had to replace the shelf to resolve that issue.