I am working on it as well. Me and my 3 friends made it to the end of the third set when one lagged out. Twice. So yeah, when you failed endure did you die or lag out? Because the second one always happens to my group.
On the bright side, if I can't seem to help you for some reason, go to www.spartan1project.com and they will help you there. Just find a run that you can go in.