Webresource.axd Doesn't Load On Application Running On Web Farm

I'm working on an ASP.net web application. I'm getting errors on some of my pages where I get runtime JavaScript errors. I've narrowed the problem down to a single ASP Menu control on the master page. I created a blank page with just the ASP Menu control. The ASP Menu control is bound to Web.sitemap. The page intermittently gives runtime errors. However, if I refresh the page, the error may or may not appear on any given page load. Sometimes, it works; sometimes, the browser throws runtime errors when loading the page or when I mouse over the ASP Menu control.

When I catch the error in Visual Studio, the message is "microsoft jscript runtime error 'sys' is undefined". When I Google for this message, I find that it is usually associated with AJAX. However, the ONLY thing on the page is a single ASP control. There is absolutely no Javascript on the page except for what gets generated by the .net framework. What could be causing this problem? UPDATE I've found out that my environment actually has load balancing with a web farm of three servers servicing the URL. When I access the application on any one of the servers individually by IP address, everything works fine.

To clarify, I understand that when a user hits the public-facing URL, it resolves to x.x.x.1. x.x.x.1 is the address for a switch which routes the request to either x.x.x.2, x.x.x.3, or x.x.x.4. When I use the public-facing URL, I find that some of the axd file requests are intermittently rerouted to Error.aspx! WTF? I'm told that this is the result of a security feature that is meant to protect me from cross-site scripting and other assorted bad stuff. What can I do? Update After taking out some error page auto-redirects, I get a more meaningful error message: ASP.NET Ajax client-side framework failed to load.