Gross, what happened to my paint!?

[Kate]

I went to get some paint out and it wouldn't come out, I knew it wasn't empty cause I could feel it when I shook the bottle and so I opened up the cap and when I did the paint was all stretchy and stuck the the cap. It seriously is like rubber, and it's not wet. What the heck happened? It's acrylic and it's not even that old! Look at it http://i781.photobucket.com/albums/yy94/ktj_1006/Picture.jpg