Onan 3600lp turns propane regulator to red

Well I installed the unit in to the RV yesterday. Got everything hooked up, bolted down and wired in. Made sure the demand regulator opened properly by hitting the prime switch and blowing a little on the vent hose. Cranked and started right up......... and then promptly sent the RV propane regulator to red and shut down. I about cried. I went through the whole process in my head. It ran just fine in the garage, what had changed. Through process of elimination I determined it was the pigtail hose. NRALIFR nailed it again. I never suspected the pigtail hose because in theory that would only effect the propane flow from one tank, not both. If the pigtail was bad on one side the flow would be fine from the other side, but both sides produced the same results. I had a long pigtail made a couple years ago so I could bring a separate larger propane tank with me on long stays. I had the original pigtail that I used with my temporary set up in the garage. The original pigtail worked fine. So, I still believe the demand regulator was not working right because the generator did not run even with the good pigtail until I rebuilt the demand regulator. It was a combination of things, both pigtails and the demand regulator. I don't know how all that could have happened unless it was caused by the same event. 99% of the time I get my propane from a large supplier here in town. I don't use gas stations or U-haul or what ever. I don't think I got bad propane, and even if I did get one tank of bad propane, how would it effect the other side pigtail? I really don't understand how it could have all happened at the same time, but it did. Anyway, thought I would follow up with that news. Going down to the propane supply house today to replace those lines. Thanks for all the help!