I wish I could help answer your question. I have not a clue about Knitmaster 155. The only knitting machine I've used so far is the USM (the ultimate Sweater Machine).
I googled around a little bit and find this site (www.theknittingcloset.com) that has all the knitting machine trouble shooting information.
Here are the forum you may what to join and ask about your machine's trouble. They're all free to join.
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