A question for Windows specialists

[jbv at souslelogo.com]

Hello list

One of my clients has a recurring problem with a standalone I built for them.
At startup a serie of lists of various data are loaded from a remote
server and
a progress bar shows the loading. And then these data are used in various
ways
in the app.
For a couple of weeks, at startup the progressbar speeds up much faster than
usual and most of the lists of data aren't loaded. Actually a couple of
them only
are randomly loaded. This happens on 2 PCs (Win 7 and XP) connected to the
same adsl line. Other people use the same app on similar versions of windows
in different offices and with different internet connexions and never met
the problem.
I did myself several tests on Win 7 and XP and everything runs fine.
The client is located 500 km away, so every ettempt to fix is done by phone.
We have disabled the antivirus software, checked for a firewall, restarted
the PCs
several times, but to no avail...
So finally here's the question : what else should we check ?
Thanks in advance for any wise suggestion.
jbv