When you get the following error message: “Printer stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)”
There is probably something wrong with any of the 2 thermistors (extruder and/or heated bed thermistor) as the printer goes into this state when it sees a temperature that is not sensible. Check the value of both temperatures, they should show room temperature when not heated. If they show 0°C or a really high temperature then something is wrong. First fix this error (probably wiring) and then use the manual G-Code entry in the manual control tab in Repetier to send “M999” to the printer. It will then be reset and you will be able to control the printer again.