CIX-100 software version 5.2. Rotary phone on an RSTU3 card.

For some reason, dialing 1 does not work. The system ignores it. Dialing 1 won't break dial tone, and if an extension ending in 1 is dialed, you get silence and then reorder. I thought perhaps the dial on the phone needs some repair, so I tried tapping out 1 on the switchook. I can dial 2-0, but not 1. Tried another working phone. Same thing. Can't dial a 1. I also tried disabling switchook recall for this station and changing the dial make/break ration. No luck.

Is there something I am missing here? And I going crazy?