Try adjusting your tension.
Some times I have to "re boot" the machine. Like turn off and re load the item. Take off the foot plate and look good for any loose threads, or burrs on the feet on the bobbin area. Other than that i don't know.
Hope this helps.

You have mention about all that I can think about at the moment. I will try as cracker says to restart the machine. Maybe it could be the embroidery design itself that is corrupted try reloading the design again.

happened to me yesterday--my top thread wasn't threaded right! took me an hour to figure it out.

Switch off the machine
Take a break, have a cup of tea and then start again.
Hope you get it working again
Seems like you have cleaned it well, What about re threading the machine with a diffenent cotton.
Good luck
Hugs
Yvonne Castelyn

thanks

every time this has happened to me...it's the top thread! Some how it had jumped out of that take up hook thingy! Always rethread your machine when this happens...bobbin & top thread. And if it is a computer driven machine, turn it off & allow it to reset. Hope you get back on track quickly!