Problem synching with exchange.

I have about 10 windows mobile devices on my network. All were synching fine
with exchange 2003 via an ISA server until recently. Unfortunately, I have
been unable to track back and find out exactly what changed to break it.

The problem is that if I connect one of my devices to a workstation it
connects, over the LAN via a proxy server, but then prompts for the user’s
password to access the exchange server. I type in the password and it all
works fine for the rest of the day. Then if I unplug the device from the
workstation it connects to the server on the internet via the GPRS connection
and again prompts for the password. I type it in and it all works fine until
the next time I connect the device to a workstation at which point it does
the whole thing again.

It’s as if the device thinks that the internal and external server are two
different servers and saving the password for one replaces the one saved for
the other one.

This problem happens with every one of my mobile devices. I’ve been
struggling with it for the past month and have completely ran out of ideas.

Can anyone help?