Use only dry paper in the machine. Moisture evaporates from damp paper due to the heat generated inside the fixing unit (it is most likely to occur at low room temperatures). This is not a malfunction, but you can prevent this by using a stack of new unopened paper.
However, if you smell something burning, immediately turn OFF the machine, unplug the power plug from the AC power outlet, and contact your local authorized Canon dealer or the Canon help line. Continued use may lead to a fire or electrical shock.