Scanner disconnected message on Canon mx850 when scanning

Hi all,
We are getting a message saying that the scanner has been disconnected when scanning documents with colour on our Canon mx850. this does not happen when we scan black and white documents. If we are trying to scan a 7 page document, it scans the first 4 pages and then throws up the message saying.

Scanner has been disconnected or has lost its connection. We have checked all of the cables and put the printer through its reboot process but still get the same problem.

Appreciate your help guys.