Condensation on the interior glass pane and / or frame and sash is a completely natural phenomenon and not something caused by a defect in your VELUX skylight or roof window.
Condensation occurs when the level of humidity indoors is too high. Condensation forms on relatively cold surfaces such as a window pane. The immediate solution is to ventilate the room, preferably a couple times per day.
Please visit
www.cmhc.ca for more information about condensation.