I have a Janome MC6600P - it is about 12 years old, are you using the thread holders on the spindle?It may sound crazy but sometimes the thread will catch on top of the spool. Also, I use Sewer's Aid on my thread. It helps the thread glide thru the machine. And my machine has been serviced twice in 12 years and the repairman didn't find any problem or build up of stuff. I clean out the bobbin area often, and put the machine oil in the wick and around the edge of the bobbin thingy. If it's not completing the stop - that sound mechanical and I would take it in. There is no reason to fight with something that may be a glitch in the program. My machine came with three free lessons, so hopefully you can get this taken care of quickly.