Configuration Conflict
Microsoft Firewall client for Microsoft ISA 2004 has an option to 
automatically reconfigure Internet Explorer settings. Unfortunately, this 
setting will cause Internet Explorer to detach from Fiddler at random times. To prevent this problem, disable 
browser automatic configuration in the Microsoft 
Firewall client.
	  
		  - If there's a Firewall Client icon
		  
 
	in your system tray, right click it and choose Configure... from the popup menu 
		  - If not, type firewall in the Start Menu search 
		  box and choose
		  the
		  
 
		  icon 
	  
	  On the Web Browser tab, uncheck the checkbox.
	  
		  