Weird problem with SP-1

[splatface]

So I was at the field, screwing in my tank directly into the gun, and it starts to shoot air out of the little hole in the bottom of the ASA. I checked the o-ring, it was fine. Put a little oil on it, tried again, same thing. So I try my brother's tank. Same thing happened, so now I'm thinking somethings wrong with the gun. So I ended up trying a rental tank, and then it worked.

Any idea of what's up? It did this on two different days, and I'm stumped.