VNC SDSL problems

[Tony Mulligan]

I have set up a Win VNC server at work behind a firewall, forwarding is
enabled for port 5900. Internet connection is ADSL static IP supplied by
ISP #1. 

I can access the VNC server from the internal network, from a dial-up
connection from ISP #1, an ADSL Static IP from ISP #1, an ADSL dynamic IP
from ISP #2,  a dialup connection from my own ISP #3 but NOT from my home
SDSL (static IP) connection (ISP #3). In all cases I used two laptops to
connect, one Linux and one Win ME.

When I attempt to connect I get prompted for a password and this seems to
be accepted. I then get a grey screen with "generating preview", then
nothing. No more packets are received and it times out.

I connect directly to the SDSL modem (no router). My ISP informs me that
their is no filtering on their end. The quirk with this SDSL connection is
the circuit between me and the ISP is carried via ATM over a separate
telco network (who bill me separately). 

Some pointers on how to troubleshoot this would be appreciated.

Thanks.


Tony Mulligan