VNC not connecting over SSH tunnel

[Gary Dale <garydale@rogers.com>]

I'm not having this problem on all machines. I can connect to every 
workstation in a remote office using:

  ssh -L 5902:<remote workstation's local IP>:5900 <remote router's 
public IP>

then in another terminal:
  xtightvncviewer -encodings "tight" localhost:5902

However, there is one workstation that I get
  xtightvncviewer: VNC server closed connection
when I try to connect.

The ssh session also shows this message:
   channel 3: open failed: connect failed: No route to host

Indeed, I can't even ping it from the remote ssh server.

However, when I went to the office and tried to connect using my laptop, 
connected into the local network, I was able to connect normally. 
Moreover, I can logout and log back in from the workstation so the VNC 
server is running as a service

It's not a machine "suspend mode" thing either. I can't connect even 
when the computer is being used.

The remote workstations are running Windows 7.

Any ideas?