recently we moved an ASP.Net 3.5 website to 4.0 (integrated mode) and when we deployed to the clients server (Windows Server 2008 Web edition) we notice that some .aspx pages are serving 404 errors.

What is strange is that

1) the pages exist

2) if you browse from the server itself the page is served as normal, only external clients get the 404

3) it's the default 404 error page not the one configured in the web.config

4) it only happens for some .aspx pages, and I've not been able to establish a link between the pages that are not being served externally.

We are using a URL rewriter module which I first thought may be at fault but then realised that only some of the failing pages are being rewritten. I've also tested removing the http module and the problem still persists.

As everything is working as expected when logged onto the server I was thinking it my be some sort of permission issue, but why would it only affect a few pages?

I turned on failed request tracking and the debug files are being generated with the expected 404 error, although at the moment I'm not sure what most of the data means so can't decipher what's going on internally.

I'd really appreciate some help with this one.