This article was previously published under Q307502
When you set up proxy settings in Internet Explorer by using the Automatically detect settings setting, the client may fail to receive the settings from an Internet Security and Acceleration (ISA) Server. This can happen even if the client gets the configuration correctly when you specify the full URL to the Wpad.dat file by using the Use automatic configuration script setting or by using the Internet Explorer Address box.
You can set up a DHCP server to use the option 252 to automatically configure proxy settings for Internet Explorer clients by specifying the URL to the server that is storing this information. The request may fail if you have configured the scope on the DHCP server with a capital letter in the URL that points to the Wpad.dat file, for example, "http://isaserver:8080/Wpad.dat". ISA Server is case sensitive and a request for Wpad.dat does not work because ISA Server is using wpad.dat.
Use all lower cases in the URL when you configure the scope, for example, "http://server:8080/wpad.dat".
For additional information about automatic discovery, click the article numbers below to view the articles in the Microsoft Knowledge Base:
252898 How to Enable Proxy Autodiscovery in Windows 2000
296591 A Description of the Automatic Discovery Feature