The printed document was poor quality. I shook the toner. Printed again. Good quality. 10 min later - poor quality again, two transparent lines in the text. Shook the toner. 'Install toner cartridge' error message appeared. Took the toner out, put it in. Everything's OK. A couple of prints later poor quality comes back. Dad comes. Takes toner out, shakes it, puts it in. The error message appears. Takes the toner out and puts it in. A couple of times. Indicator light still red.