GarageDragon

It is driving me crazy and I can't seem to fix it! I've started my very first FMQ on an actual quilt, having been happy with my practise sandwiches, but the thread just keeps snapping. The tension seems fine (I think). Just to complicate, although I usually use the Gutermann poly thread, I'm using their cotton thread, because I wanted the variagated, and it only seems to come in cotton. Could there be something I should be doing differently?

Thank you for any suggestions (particularly any that don't involve ripping out and starting again with different thread - I really like the look of the threads I chose)