Can't add to dock

I am trying to add a new stack to my dock, but it won't let me. When I drag the folder to the dock, it shows what programs will try to open it when I hover over the apps, but when I release the mouse, it just goes back to the finder window (the icons in the dock don't separate like it knows I am trying to add something). I have tried this with a folder of apps as well as a folder of documents...

Also, when I try deleting something from the dock by dragging it off the dock, it shows the symbol with the icon (the "poof" or whatever it is!), but when I release the mouse, it goes right back to the dock. It also does this when I drag it to the trash. The only way I can remove anything is by click and hold on the icon and choosing remove from dock. It would be so much easier to just drag it off.