If you have accidentally applied markings with permanent marker on your whiteboard, they can be removed with ethanol, methylated spirit or isopropanol; for marking applied with paint markers, use a benzine cleaner, for example. Please keep in mind that edding permanent marker or paint marker can only be removed from smooth, non-porous surfaces.
We recommend you test on an inconspicuous area first to see if the surface is sensitive to the solvent.
The most gentle way to clean your whiteboards is with MagicWipes, which only require a little water, are reusable and can remove whiteboard and permanent marker inks.