The remote server returned an error: NotFound

when trying to make simple POST request to a PHP page. I’ve spent half a day diagnosing this problem. And solution was found entirely by chance, because exception messages weren’t helping in any way. I mean, I was always getting abovementioned error message, without any details (what host, what page, request parameters, etc). But enough of complaints, let’s proceed to the solution. The troublesome code was this one:

var _request = (HttpWebRequest)WebRequest.Create(_svcUri);
_request.Method = "POST";
_request.ContentType = "application/json";
_request.Headers["sid"] = SessionID ; // <==== this line

SessionID was null at the moment and this made HttpWebRequest so pissed off that it even wouldn’t send request header to the server ! And because of this, Fiddler was completely useless here. After adding necessary check, everything started working like a charm.

I hit Ctrl-Ctrl (very handy shortcut of Google Desktop, that summons search bar) and pasted the error text there. First, I came across this article. I followed every step in it (some of them twice :-) ), but it didn’t help. So I kept searching.

Then I found this interesting site. Performing this step didn’t help me either. I have installed Fiddler and it finally shed some light on the problem. There was an error while requesting xmlrpc.php (which is used by external systems, such as WLW, to talk to WordPress).

Warning: include_once(/home/tulentse/public_html/blog_technical/wp-includes/class-IXR.php) [function.include-once]: failed to open stream: No such file or directory in /home/tulentse/public_html/blog_technical/xmlrpc.php on line 55
Warning: include_once() [function.include]: Failed opening ‘/home/tulentse/public_html/blog_technical/wp-includes/class-IXR.php’ for inclusion (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/tulentse/public_html/blog_technical/xmlrpc.php on line 55
Fatal error: Class ‘IXR_Server’ not found in /home/tulentse/public_html/blog_technical/xmlrpc.php on line 108

I navigated to that file and saw that the name is in lower case (and case matters on Unix-based systems). It was joint effort of me, who checked "Convert filenames to lower case" option and Total Commander who did what I told him.

Now everyone’s happy :-)