Sorry to hear that a belt broke. First I've ever heard of someone breaking
a belt this way. Was it a "normal" timing belt attached to a stepper motor
or some other sort of belt? Timing belts are normally very strong.
You need to PHONE MBI support. They are notoriously slow about tickets
submitted online. (But maybe Tiffany our moderator will see this and
BTW, were those 20 x 20 x 10 mm calibration cubes you were printing? They
looked a bit hollow. Just wanted to mention that if you were printing them
for purposes of adjusting the feedStockMultiplier in Makerbot Desktop, then
they should be printed completely solid (i.e., 100% infill).