make sure you use a metallic needle, loosen your tension a little (just like using invisible thread) and slow down. use a bobbin thread in the bobbin. the needle is the most important the metallic needles eye is shaped to keep from fraying the metallic threads. and if you sew too fast the thread stretches and breaks like invisible thread will.
good luck...i think metallics are a major pain in the ****
but when you are successful with them they sure make some beautiful stitching!