Agree with Jim about the yellow-dot case. I got some wonderful butterflies from Urban Threads, my absolute favorite source for embroidery, and tried the yellowdot case since I was using thread that matched my lace embroidery. What a mess the yellow-dot bobbin caused! I switched back to the regular bobbin, and all was well. I was never able to stitch out lace using my old Bernina 200 upgraded to 730, but the Urban Threads designs are practically foolproof and amazing. When I finally got the regular bobbin using embroidery thread to match my design, all was fine.
STILL, when I was doing something other than lace, using regular embroidery bobbin thread, the machine (15000) got terrifically fussy and balked at the bobbin thread I had used successfully for ages. There's a definite learning curve, and that's fine, but it would be seriously nice if Janome spelled things out for users and gave them actual tips on when to use what sort of bobbin thread and WHY! Knowing WHY is always helpful. (Just FYI, I tossed out some money on AUTHENTIC Janome embroidery bobbin thread, so I am TRYING to do things "right.")
While I'm here on embroidery designs, I have mainly used size 11 embroidery needles, BUT many stabilizer companies suggest using the correct needle compatible with the fabric. So, if I'm embroidering on a knit, should I really be using a ballpoint needle for embroidery? The whole process gets very confusing, and the time consumed by making mistakes on my judgment calls is not only irritaing but costly in terms of expensive stabilizer and hours of my time wasted.
Not sure what the problem is with your existing bobbin thread, more details needed. Size 11 needles are fine as long as you are using 40wt thread, but when the thread gets larger so should the needle. Diane uses the "cobra head" needles (Janome purple tip) for pretty much everything. They are a ball point and work really well.