When I try to print with my Brother PT-1200 label maker, it says "ERR" and does nothing. I changed batteries and the label cartridge but still nothing.

Open the back of the label maker. remove the cartridge. in the lower right hand corner of the where the cartridge fits, there are 3 little posts that are pushed in when you insert the cartridge. find the holes on the cartridge that fit over those posts. cover the holes on the cartridge with tape. reinsert cartridge. try again. worked for me. If you push in the posts individually, you can figure out which one is giving you the error message. I'm not sure that it really makes a difference. I taped over all three holes and it worked fine after that. i realize its not a perfect fix, but may allow you to print anyways!

I changed the cartridge and batteries and still had problems with only 2 vertical lines printing. I stopped using the electrical cord, changed the batteries again and it's now working. Each time I finished using it (which isn't a lot) I take the batteries out and put them back in prior to the next use and that seems to work. It's inconvenient, especially having to keep the batteries used with the label maker, but at least it works.