First thing to do, is too add an exclusion for Web in your web.config.
Unfortunately, I haven't managed to find much of a pattern to it. You can break a working client, and you can fix a broken one, but it's kinda random.
I know that's a fairly useless way to start out, but it gets better, I promise.
From IIS Manager, select the properties for your application's website, and goto the 'Home Directory' tab.
Click 'Configuration', then bring up the list of extension mappings on the 'Mappings' tab. AXD, and if that's not there you need to create it.
There are a few things which can go wrong with Web
Some of these are specific to compression (and in my case, the compression I'll be writing about is pretty specific to the Blowery module, however you might find some of the symptoms apply to other compression techniques), some are specific to Network Load balancing (NLB), and some are specific to IIS.
The first thing to do if you're having the Java Script errors is to determine if they're being caused by a "missing" Web Do this in a client which is working, and you'll get a file filled with Java Script functions - funny that. My only thought is that these people intended you to update all the pages in your application and included a hardcoded reference to this file. If you view the source of a lot of your pages, you'll notice that the include to Web is made only on pages which need it. NET Framework decide these things rather than having to go through an entire application and work it out.
Simply view the source of the page which is breaking and find the js include line which references Web During my googling, I came across a few people who recommended simply getting the Web from the cache of a working client, and copying it to the root of your application. Compression If you're running compression, you can confirm whether it's causing the problem by temporarily disabling it entirely.
The important thing is to make sure "Verify File Exists" is deselected, as shown here: If you have load balanced servers, then make sure you repeat this for all servers.