Paul,

> Now a second customer has installed new equipment and the same thing is
> happening there, while it worked fine before they made the change. Their
> support guys tell me they dont think there are any relevant settings in the
> firewall, router, server etc.

What exactly is "new equipment"?
If the change in behaviour occurred at the same time the "new equipment"
was installed, it's likely the "new equipment" causing the trouble....

High likely of course, not for sure...

,g. the moment my router was remotely (by the ISP) updated with new
firmware, the NAT-behaviour of this router was slightly changed and some
(not all) customers could no longer use the the services from one of ny
servers... It was like finding a needle in a haystack, because "nothing
relevant was changed, honestly"...

John