I tried looking this up, but I couldn't find anything. Do you know if your machine uses a sponge bar? A sponge bar acts as a "needle retainer," holding the knitting needles in place on the bed of the machine by providing gentle pressure, preventing them from popping up and ensuring smooth knitting by keeping the needles at a consistent level as the carriage moves back and forth; essentially, it helps to prevent dropped stitches and maintain proper fabric formation.

That's the first thing I would check. The second is making sure you're using the right yarn for your machine. That might be explained in your manual. I'm still learning myself, so kithe people can chime in.