This has happened for a few reasons on us. The most simple fix to get the key out is to flip out the little tab on the base of the shifter that has a picture of a padlock on it and stick a pen down in the hole and press the reset button to reset the security lock. Most of the time it's because of a low or weak battery. I haven't heard of anyone having problems with the actual ignition lock system itself, but I've had sillier electrical problems on GM vehicles. Either way, reseting the system should release the key so you can go on about your business for the short term.