Try BAFs MLS Grabber in the link below. It should pull your MSL for you. Sounds like it somehow got changed in the switch. Did your new carrier program or flash the device in house to work on thier network?
http://forum.ppcgeeks.com/showthread.php?t=43560
You gotta post in the right forum though... this thread will get moved to the main Touch Pro forum. This one is for ROM / RADIO upgrades.