I Narrowed it down to:
For some reason
bmap_create seems not to be able to load bitmaps from a path,
but can load them direct from bin folder OK.

Path:
public static String textures = Application.StartupPath + @"\defaults\textures\";
and use like so:
water_bump = BMAP.bmap_create( textures + "waves2.tga" );

All other load or create commands load from these types path fine, but bmap_create does not.

Would not seem to be a wrapper problem though.