could be the "fadeLength" parameter, try making it 255. Maybe make the width a bit more to see it easier too
heres what i use for drawing a waypoint (try copying the values)
Code:
g_pEffects->Beam( m_vOrigin - Vector(0,0,WAYPOINT_HEIGHT/2), m_vOrigin + Vector(0,0,WAYPOINT_HEIGHT/2), CWaypoints::waypointTexture(),
0, 0, 1,
1, WAYPOINT_WIDTH, WAYPOINT_WIDTH, 255,
1, 0, 0, 255, 200, 10);
the waypoint origin is in the center so i draw from -36units to + 36units