I found the problem as I debugged down into MapLabelLayer.cs, the PlaceLineLabel method expects a basic geometry of type LineString but this particular layer i am feeding it consists of MultiLineString features, not the first time shapefiles containing multiline feature cause problems in my experience.
As we have a policy of only using officially released components in this application, i am stuck with release 1.8 and fixing this in the current trunk of DotSpatial is not a solution for me, i'll see if i can cleanup the features and try to convert them to regular linestrings within our application, for now....
As we have a policy of only using officially released components in this application, i am stuck with release 1.8 and fixing this in the current trunk of DotSpatial is not a solution for me, i'll see if i can cleanup the features and try to convert them to regular linestrings within our application, for now....