You don't appear to have an adjustment screw on your gripper (its on the back and can loosen or tighen the "grip" on the string.
I had a different issue with mine (the tab holding the screw snapped off) contacted Herb and for $12 + shipping (could be more now) I recieved a new gripper for my machine with instruction on how to replace it. The instructions were excellent and I was up anbd running in about 10 min.
You'll need to send him the vesion number of you wise (on the top ) and photo's of your gripper. Tell him you want one with the adjustment screw on it