graphic symbol keeps turning into object when I insert keyframe

Hey, so i was in the middle of some puppet rigging via the parenting tool, and while trying to make an arm move I kept getting the "current frame needs to be converted to symbol to insert tween" message. I thought I had accedentally drawn something extra into the layer but cant find anything, and when I click on the symbol it shows as a symbol in the property pannel, but when i click on the layer the symbol registers as an object. Any Idea of whats happening?