I was reloading the string on the string trimmer and went to put the head back together and now for some reason the tabs won't go in far enough to lock into place. I've done this several times and never had this problem. Examining the head, it looks like the ring with the tabs on it moves freely both rotating, and also up and down, which means the tabs are out of reach of the slots when I push the head together. I can't recall if the up and down is new, perhaps something broke allowing that movement that pushes the tabs out of reach of the slots? I hope this description makes sense.