I have a C5100 Oki laser which i cleaned with an air compresor resently. Ever sinds i keep recieving a 541:M toner Sensor error message. I have replaced the toner with a new one and still same problem. Any sugestions ????
On the toner cardridge, in the blue handle, there is a square hole with a white thing behind it, which moves back and forth when the stirrer inside the cartridge is turned (via the gear). This is part of the toner level detection. In the printer, where the blue handle is locked in place, there is a light sensor which "looks" at the little white thing, and detects if it is moving back and forth or not. For this to work, A) the white thing must be clean and B) the light sensor must be clean. Probably some toner or dust has gotten onto one or both of these places, with a quick blow the problem should be fixed.
This is also the reason why the starter cartridges cannot be refilled with refill toner, like from http://www.farblaser-toner.de - they only have a shiny piece of tin foil instead of the white plastic flag, so when the first cartrige has been used up, the printer insists on a moving sensor, so you need to get a new one which has the toner sensor in it, then this one can be refilled as often as you want.
Hope this helps!