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Please follow the steps below :
Sometimes following the steps below, solves the problem, if it does not solve the problem, then you may have to took off the scanner cover, readjust the scanner unit, fixed the lamp contacts etc.but remember this steps are extremely risky, if you do not have prior experience in printer repair, so be careful, before doing this .But in any case, at this point, your printer will either have to be serviced/fixed, or else replaced and recycled.Please recollect whether your printer is older than 1 year old (if so, its repairs may be done for free by Canon under its standard warranty coverage of its printers). To find out how much its repair would cost you, you may use the form on this web page, to request an estimate for repairs:http://usa.canon.com/cusa/consumer?pageKeyCode=repairLandingNow, here are the steps, that you can follow first and if this does not solve the problem, then the steps to dismantle the scanner part is mentioned below.Turn the printer OFF, when it is on, by suddenly and sharply unplugging it from the power source.Also unplug the USB cable after this, if you use an USB cable.Wait for 10 minutes.Plug it back in.Turn it on if it didn't turn itself on. Wait for it to initialize.Here is the dismantling guide of the scanner part, please be sure to take risk, because, if you do something wrong, then I will not be able to help you further, as I cannot see your printer.To open the scanner unit,1) Detach the ADF from the top of the scanner2) remove the four screws at the top rear of the scanner unit3) remove the left and right control panel covers. There are six snaps (3 top and 3 bottom) on each one. Look for the MP810 Service Manual (as I do not have the soft copy present in my PC, which I provide) for photo illustrated directions. I started at the bottom, once that was free I pulled gently and the top snapped out relatively easily.4) remove the four screws holding the control panel unit and pull the control panel out part way.5) remove the two screws under the control panel unit.6) with a small flat screwdriver gently pry the top half of the scanner housing up, go around the edge and when you come to a tab try to push it in.Now you can clean the glass. BE VERY CAREFUL NOT TO DISTURB THE SCANNER UNIT ITSELF - DON'T PUSH IT BACK OR FORTH ON THE RAIL OR IT WILL LOSE ALIGNMENT.
Please note: this is a hardware error with your Printer.