First, it's great to see someone who took the time to debug it all the way down to that line of code, lol - thanks :-) .
A couple things to check:
- Are all the resistors in place? Not having the 2.2kΩ pull up resistors on the I2C SCL and SDA lines would cause this problem.
- Have you wired the Teensy USB to the board USB, and are you plugging into the board USB? If you haven't done this (and you also haven't jumpered the Teensy VCC to the board VCC, which would be another, but much less common, option) then the board isn't getting power, which would mean (among other things) that the pull up resistors weren't actually doing anything.
Since the Teensy is working, and assuming that nothing abnormal is going on, these are the only two things I can think of that would cause this exact problem. Please post back with whatever you find :-) .