Many of us have had problems with the ACME propane connector.
But, what I would try first is just turn both tanks on and leave them on for a half hour or so (so pressure can equalize) with no load at all on them. Make sure the selector lever on the auto-changeover valve is all the way left or right. If you get propane in one direcion, try the other to see if you maintain pressure. Let us know how you make out.