I switched my PLA roll to the right and printed a part and it worked after about 4 failures. Anyway, now I put some ABS on the left side and setup the Makerbot Desktop software to print with JUST the left side (including the rafts and supports). The annoying part is that it still heats up both extruders which causes some PLA to come out of the right during printing and the motion of the head going back and forth drags this PLA nobbind messes up the first few layers of the print. It's so annoying that they don't make it easy for you to use the left extruder. It's like they want you to use the right for everything.