If you deploy vnc using a depoyment profile using a non standard port (5901) for example.
When the object is created in the managed group, the object's vnc settings are still at the default 5900. You need to manually change this to the new port before you can connect to the client
even if the managed group properties has been changed, the objects port is not updated unless you rescan the object.
i have reported this issue many versions ago but it has never been fixed.