Tifaustin - hi, I was having the same problem before with a Ryobi unit. The first error/problem I discovered was I fed the string in the wrong way. (My unit allows new string to be installed without removing the head...but you have to feed it CCW and I was feeding it CW.) Then, after taking the head off to give the unit a good cleaning, I caused myself another problem - I tightened the nut that holds the head on too tightly. That prevented the automatic feed from "bumping" properly to feed the string.

I don't know if either of these will help you but they're good things to check out. Also, yes - if the string gets too old it can start to jam. The plastic string can get warm while the unit's operating and will eventually get stiff/brittle. It can also become slightly too large to allow the automatic feed to work right, or so I was told. Regards! Jim D/Heathsville, VA