VNC broken down suddenly in Windows Server 2003 R2

[Seak, Teng-Fong]

    I've installed VNC Free Edition 4.1.2 in a Windows Server 2003 R2. 
VNC is a service.

    Sometimes, without any visible reason, the VNC server is broken
down.  By that, I mean:
1. No connection can be established.  (I should have jotted down the
error message I got from the client side, but I forgot.  Right now VNC
is working)
2. The VNC icon in the system tray disappears as well.

    I had tried to look in the event log but nothing there.  I had tried
to restart the server by going to Start menu > Realvnc > VNC Server 4
(Service-Mode) > Stop VNC Service.  Then ..... > Start VNC Service.  But
this doesn't help.  I had to restart the whole machine to make it work
again.

    I'd like to give you more info, but since there's no error event, I
don't know what to do.

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