It seems that c# bindings were not updated after the engine was. The new function is called h3dShowOverlay
s and has less (and different) parameters than before.
New Function:
Code:
 
void h3dShowOverlays( const float *verts, int vertCount, float colR, float colG, float colB,
                          float colA, H3DRes materialRes, int flags );
Old Function:
Code:
 
void h3dShowOverlay( float x_tl, float y_tl, float u_tl, float v_tl,
                         float x_bl, float y_bl, float u_bl, float v_bl,
                         float x_br, float y_br, float u_br, float v_br,
                         float x_tr, float y_tr, float u_tr, float v_tr,
                         float colR, float colG, float colB, float colA,
                         H3DRes materialRes, int layer );
For more info check documentation or look for this function in Horde3D.h, that is located in <SDK Folder>/Horde3D/Bindings/C++/