This issue has been mentioned before, but I believe it to be the cause of several other problems as well. Basically, the ASP.NET hosting process ignores the first header of any http request. This will cause various things to fail if they depend on reading the value of the missing header.
TEST CASE
Save the following page as AbyssTest.aspx on an Abyss Server configured with ASP.NET 2.0 (this just prints out all of the headers that are seen in the HttpRequest:


<%@ Page Language="C#" %> 
<%
	int loop1, loop2;
	NameValueCollection coll;

// Load Header collection into NameValueCollection object.
	coll=Request.Headers;

Response.Write("All HTTP Headers:\r\n\r\n");

// Put the names of all keys into a string array.
	String[] arr1 = coll.AllKeys; 
	for (loop1 = 0; loop1<arr1.Length; loop1++) 
	{
	   Response.Write(arr1[loop1] + "\r\n");
	   // Get all values under this key.
	   String[] arr2=coll.GetValues(arr1[loop1]);
	   for (loop2 = 0; loop2<arr2.Length; loop2++) 
	   {
	      Response.Write("\t" + Server.HtmlEncode(arr2[loop2]) + "\r\n");
	   }
	   Response.Write("\r\n");
	}
%>

From the command prompt, telnet into port 80 of the Abyss server configured above (replace 10.0.1.6 with the IP Address of your server):


telnet 10.0.1.6 80

Enter the following http request replacing 10.0.1.6 with the IP address of your server (make sure to press enter/return twice after the last header):


GET /AbyssTest.aspx HTTP/1.1 
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.13 
Host: 10.0.1.6

This is the expected response from the server:


HTTP/1.1 200 OK
X-AspNet-Version: 2.0.50727
Set-Cookie: ASP.NET_SessionId=i4drvturm3j4hayv4cuj1n55; path=/; HttpOnly
Cache-Control: private
Content-Type: text/html; charset=utf-8
Content-Length: 149
Connection: Close
Date: Mon, 24 Mar 2008 13:48:13 GMT
Server: Abyss/2.5.0.0-X1-Win32 AbyssLib/2.5.0.0

All HTTP Headers:

Host
	10.0.1.6

User-Agent
	Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.13

Connection closed by foreign host.

This is the actual response from the server (notice that the User-Agent header is missing):


HTTP/1.1 200 OK
X-AspNet-Version: 2.0.50727
Set-Cookie: ASP.NET_SessionId=osw3as45nh0x2wf4luznfd55; path=/; HttpOnly
Cache-Control: private
Content-Type: text/html; charset=utf-8
Content-Length: 40
Connection: Close
Date: Mon, 24 Mar 2008 13:48:37 GMT
Server: Abyss/2.5.0.0-X1-Win32 AbyssLib/2.5.0.0

All HTTP Headers:

Host
	10.0.1.6

Connection closed by foreign host.

PROPOSED WORKAROUND
If you insert a 'dummy' header before the first 'real' header, the output will be correct:


GET /AbyssTest.aspx HTTP/1.1 
Dummy: blank
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.13 
Host: 10.0.1.6

I believe that the issue could be worked around by inserting this dummy header into the request that is handed off to the ASP.NET hosting process.[/code]