You likely switched the beer and gas posts. They look the same, but aren't.
Yup, that's my guess as well or you flipped the dip tubes.
Degas, check posts and tubes,
I read this last sentence about ten times and kept thinking, there's an AHA member named Degas?
Anyway, I bet this is my problem. The posts are on the right place and it's not a hoppy beer, but I suddenly thought, I bet I switched the tubes. Though I wouldn't rule out gunk. In any event, another useful Forum thread. I will "Degas" the keg and make sure the tubes are in the right place and blow out the tubes and make sure there's no ice and so on.
Clearly I need to name this Edgar's Cream Ale...