Paper tray at front of scanner will not lift. Scanner has been reset multiple times and computer rebooted as well. Error msg= unknown error canon DR-6080/7880/9080C driver versioin 1.3.10502.17001 (-4523)

It's usually a software conflict.
If you have multiple scanning programs, the one of them may have it locked. Especially if you have a scanning program that runs as a service.

It sounds like you diagnosed it.
The tray "paper detect sensor" thinks it has paper in it, and if it doesn't have paper in it...there's a problem with the sensor.
Take the tray off and inspect the sensor. Blow out around the sensor and it's PCB and make sure it is not out of position. Check the sensor lens for anything blocking it, and retest. If it still shows always on, then replace the sensor. Press the "count only" button to illuminate it, and press the "start" button. If the scanner works properly (tray lifts, pulls paper through the scanner, and counts it)...well then you have software or connectivity issue.

Hope that helps,
Scan-R-Store Scan Store provides service and maintenance contracts on all Canon Fujitsu...

Clean the 'black dot' in the centre of the paper tray. There is an optical sensor under that. The tray will lift even without paper, but will go back immediately.
If the scanner stops after 3 pages, check disk space in your computer. If you are scanning in TIFF uncompressed, it takes lot of space. For color and Grey try JPG format, for mono TIFF G4 is the ideal option.
S. Mohan, Chennai, India

A01 is pickup error. Clean the paper sensor in the paper lifting tray and try. Clean the rubber rollers also.
S. Mohan, Chennai, India

Clean the two 'black dots' in the paper tray, just under the roller. They are actually paper sensors. Try 'page counting'. If this works, the scanner is okay. If the problem still persists, try reloading the scanning software.
S. Mohan, Chennai, India

Please explain the problem more clearly.
Switch on the scanner, load some papers and try 'page count'. If it works, then there is no problem with tray lifting or paper movement. If this is not working, try 'Qumatool' and give a command to lift the paper tray. If it lifts, then the problem is with a sensor under the paper lifting tray. (It may not be in HP - Home position). If the tray is not lifting, then you may have problem with motor. S. Mohan, Chennai, India

Error 51 is a paper jam code. Remove the paper tray in the front and the jam clear cover in the back (the light gray plastic piece in the center of the rear of the printer) and pull out any paper you can see.

Once you've removed the paper, the jam code should clear on the display, but if it doesn't, try resetting the machine. If the jam code is still there, that means there is still paper somewhere inside the machine. Check again to make sure you didn't miss any, and also lift the scanner bed to see if you can see any paper under there. (To lift the scanner, lift up with the tabs on either side until the scanner locks into place.)

There is a paper sensor just under the rolers in the lifting tray. Clean the area thoroughly with a damp cloth. Keep some sheets and try ]count only'. If it works then the sensor is okay, then you can try your scanning. If it is not sensing paper, check the sensor or connections to the sensor.
S. Mohan, India

On the right side of the scanner there is a motor just behind the small bulge in the cabinet. The motor lifts the paper tray through a bevel gear. Incase the palstic gear is damaged, it maynot lift the tray.  U may need to change the gear.
Even if the tray is overloaded, the tray will not lift.

S. Mohan, Chennai, India

Lift up the black frame around the large soft grey pick rollers on the upper part of the paperfeed until it locks into place. Power off scanner and back on and the trya will lift and the paper will feed.