This guide lets you reset the counter of  Brother DCP-6690CW Printer with the following message
"The message unable to print 50"

Follow the steps

• Lift cover
• Remove the two plastic panels covering wires
• Mark down position of cables then remove them
• remove the now-freed top scanner section entirely
• Remove screws from top plastic shell
• Two in the back and four in the front
• Two plastic tabs in the front that must be bent aside before you can remove the top shell
• Gently put the encoder strip back in its plastic guide.