K2 problem in yourshop.com

As seen in the quick start, i tried to add a category in k2 and an image for it. But guess what?? it didn't let me do this, same problem at the aricles. So if you would like to help me, it would be nice.
I've google it and a lot of people have the same problem.

PS: in the quickstart you did it. HOW?????