I had this problem and searched and searched google and HBT for an answer, and the only answers I found appeared to be either get someone to help hold the keg while straining to remove the post, or use an impact wrench--or hammer on a non-impact wrench.
There's another way, if you have a 1x2 board lying around (I'm sure a narrow piece of plywood would work, and similar).
All I did was lay the keg on its side, used the 1x2 to act as leverage against the ground, and the post came loose quite readily. Here's a couple pics to show what I mean:
There's another way, if you have a 1x2 board lying around (I'm sure a narrow piece of plywood would work, and similar).
All I did was lay the keg on its side, used the 1x2 to act as leverage against the ground, and the post came loose quite readily. Here's a couple pics to show what I mean: