>and use this object to do the work. It could well be that the machines causing problems are on a subnet using an uncooperative proxy server or are more firewall-restricted than other parts of the client's network. Any additional suggestions you can provide would be much appreciated.


Basically any application that provides outbound internet access should ALWAYS provide connection configuration information. At the very least authentication and basic mode selection (most Microsoft Web interfaces support some way to tell how the proxy configuration is handled). Usually you'll want to set the settings to use IE's settings. I'm not sure if XmlHttp can do this or not - the connection settings are very limnited. WinInet and WinHTTP both can as can tools like the MSSOAP toolkit.
Either way, manual proxy configuration options should be provided because sometimes the IE settings just don't work and a manual config is required.

+++ Rick ---