When you run 2 esc, you are supposed to pull the red wire out of the RX plug on one esc so the 2 bec in them don't fight over trying to power the rx. Lift the tab and slide it out and just heatshrink or tape it out of the way. It'll smoke the bec inside one of the esc fairly quickly if you don't.
It gets even more important when running 2 isolated battery packs, or external bec.
http://www.rccrawler.com/forum/elect...otors-etc.html
If that doesn't get it, post a pic or wiring diagram of your setup.