VNC remove control of Mac OS X Tiger desktop - use UltraVNC

VNC works great with my new Mac Mini running OS X Tiger (10.4.2) and Apple remote desktop as long as you use the VNC viewer from UltraVnc -
http://ultravnc.sourceforge.net/

For some reason the VNC viewer (V4.0) from realvnc.com did not work for me. It asked for the password and then exited.