Brother knitting machines have an ongoing punch card reader problem (timing belt/punch card reader mechanism) that can occur with Brother (and KnitKing) punch card machines. Especially vulnerable is the KH-260 (or KnitKing PC) . It mostly occurs when the patterning mechanism has not been used in a while or has not been serviced for some time. It needs to be kept oiled. Cleaning and lubricating your machine should be done regularly at least once a year and more often if your machine is used often as it is susceptible to lint and yarn fuzz contamination. Oiling the timing belt sprocket mechanism is very important and should be done regularly - at least once a year..
There is this guy and his wife that have made many videos on repairing or servicing your machine for you DIY'ers. They are friends and customers of ours and have a U-Tube video website that can be seen using U-Tube. To find them use your search engine mechanism in U-tube and look for "The Answer Lady" and/or "Ask Jack". While Jack is not taking on any new repairs at the moment, he shares his many experiences and knowledge via U-tube for DIY'ers that is second to none.
Here is a link to Jack's video on Brother Punch Card servicing that should help most anyone who wants to learn how to repair their machine and has a little mechanical knowledge. I think they do a great job with this video and would recommend it to anyone who has a Brother knitting machine. Here is the link: https://www.youtube.com/watch?v=Q-rEZP0I7h0
Hope this helps. Good Luck!