Ryobi string timmer head question

I have the RY28140 which came with and has the SS26 attached. The problem I have is with the SS26. It will not feed in new line to the other side. I made sure the arrows were lined up and it will go in one end but not come out the other end. There may be some line still in the head - so I attempted to remove the red retaining knob. The red retaining knob will not come off. At first, I turned it counter-clockwise and it was very tight. It loosened up but then I noticed to remove this retaining knob I need to turn clockwise. It will turn clockwise however I have turned it for over 10 minutes and it never gets any looser. It turns, and then clicks a bit, then turns again, and clicks, and so on.... I am sure there is extra line left in the head but the retaining knob will not come off. Anyone with any advice, let me know.

--*Rob

 

Sounds like the plastic knob has stripped where it is molded over the bolt head.