I've been field stripping and cleaning my Glock for a long time and never had this happen before. Somehow something got screwed up when I put the recoil spring and slide/frame back together and now it won't work, and I can't use the take down pin to take it apart.
Here is a pic of what is looks like now:
probably have the spring in backwards.
If the gun is NOT LOADED point in a safe direction pull the trigger and see if it will come apart.