I'm not surprised that the magazine was the issue after seeing it. Don't discard it, it may still be salvageable. Go over to Lugerforum.com and look up G.T., he can work miracles with magazines. The mag you pictured would be the correct era for your Erfurt sans the ugly white base.
Thanks - he has already given me pointers on breaking down the gun.
BTW, it shoots pretty good. Mag arrived today and I went straight to the range. After 4 rounds at 21' to sight it in and get used to the recoil, here's a 30' target, 10 rounds.
I had read many recommendations for the Winchester White Box 124 grain 9mm ammo for the P08 pistols and that was my choice when I shot mine. It worked flawlessly. It's probably a combination of the velocity and recoil impulse of the 124 grain bullet that the gun was designed for. There are probably other brands that will work satisfactorily, likely the S&B, Fiocchi and GECO. Glad to hear that the Mec-Gar magazine solved the problem.