New Post: Polyline Labels not working

I've just run into another problem - I can't get labels to appear on polylines.

shape->Labels->set_FrameType(tkLabelFrameType::lfPointedRectangle);
shape->Labels->FrameVisible = true;
shape->Labels->set_Positioning(tkLabelPositioning::lpCenter);
shape->Labels->Generate(L"[Name]",tkLabelPositioning::lpCenter, true) ;
shape->Labels->Visible = true;

The above works for point shapefiles and the labels appear, but I think I am missing something with polylines.... I seem to remember that there were some extra steps involved, but that may be me misremembering.
I've tried GenerateLabels but no joy.
I've looked through the examples and can't seem to find anything about polyline labels.
I'm using the latest version - 4.9.4

Any help appreciated

regards

BB