If you already know this for a fact, then try skipping down to the thread "Show Us Your Dutch Bikes" and scan those 43 pages to see if you can find anything matching...it doesn't ring a bell with any of the major Dutch brands I'm aware of.
Also try contacting one of the NL- or Belgium-based members who may know far more about Benelux brands than me (but you have to get to 50 posts before you can use the Personal Messaging feature).