Renamed logingoed_tekstStyles2.xml to logingoed_undefinedStyles1.xml, cleared my IE cache and browserhistory and then it found the stylesheet. But then other problems occurred e.g. it would not hold the styles in the page.
Despite of all the nice features it is supposed to have, it takes too much efford to get it working.
So, never mind about finding a solution as far as I am concerned. It will just not work properly. I removed the HtmlEditor and started using the DMXzone editor again. It does not have that much features, but it will do what is it supposed to do.