Hi Jari,
I've tried to explain the process a bit here to remove some of the "unknowns".
In the Maps example,
General Map.
The CapeSoft Offices Marker has been added with the following JavaScript;
$("#GeneralMap").ntmap("addMarkerToMap","_home_",-34.041,18.47,{icon:blueMarker},"CapeSoft Offices", 1);
If you right click on the page, you'll see this in the source of the page.
That line of JavaScript was generated by the generated line of Clarion code;
p_web.Script('$("#' & p_web._jsok(p_web.nocolon('GeneralMap')) & '").ntmap("addMarkerToMap","_home_",' & p_web.GetLatLng(-34.041) & ',' & p_web.GetLatLng(18.47) & ','&p_web.WrapOptions(loc:options)&',"'&p_web._jsok('CapeSoft Offices', Net:HtmlOk*0+Net:UnsafeHtmlOk*0)&'", 1);')
the maps widget is in jquery.nt-maps. This is a jQuery UI widget, and many of the JavaScript files follow this pattern.
addMarkerToMap is obviously the first method to inspect. The first parameter to this javascript method is bidv, which, as you correctly surmised is the marker "identifier". it is, incidentally, case sensitive.
there is a removeMarker method, but alas, it's removing from a cluster, not the "unclustered markers" (an oversight I'll need to fix.) which brings us back to your original post;
Notice you used _MyMARK_ when creating the marker and _MyMark_ when removing it.... Alsas, as mentioned it's case sensitive, which is why it didn't work.
sorry for not noticing that earlier.
cheers
Bruce