You may have already got it fixed or just don't use needle #1. If you have hit a hoop it will cause this. Take the front cover and top off the machine. At the top of the 4 needle bars there is a screw. Look to see if the screw on needle #1 is lower than the rest. You should be able to compare with the other 3 needle bars. Loosen this screw and slide it back up even with the others. This lets the needle bar go lower and hopefully this will fix your problem.
Answers & Comments
You may have already got it fixed or just don't use needle #1. If you have hit a hoop it will cause this. Take the front cover and top off the machine. At the top of the 4 needle bars there is a screw. Look to see if the screw on needle #1 is lower than the rest. You should be able to compare with the other 3 needle bars. Loosen this screw and slide it back up even with the others. This lets the needle bar go lower and hopefully this will fix your problem.
I suggest you call a Janome dealer and ask them your question.