Happens to me quiet frequently.
What happens is when you push the button in, it moves a lever in the ebrake mechanism. The stop for the lever gets bent open, and the lever gets stuck against that stop.
What you have to do is take off teh ebrake boot. Then you should see a little lever, in my car it's black. It's pretty easy to spot against the metal. just push that back up into the mechanism. that should release the button. What i'd do after that is get some pliers and carefully bend that metal stop so it actually stops the lever, instead of getting it stuck.
if you need more help lmk, i can get pics if you really need them. (i might not check back in the thread so just pm me)