When adding an application mapping for aspnet_isapi.dll, I noticed when invoking an webservice IIS would throw a 404. This is due to a flag being set to 5, which is the default. Either by editing the MetaBases XML in IIS6 or modifying the MetaBase in IIS5 with MetaEdit. You can alleviate this by setting the flags to 1 rather than 5…

.asmx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
		ScriptMaps=".asa,C:\WINDOWS\system32\inetsrv\asp.dll,5,GET,HEAD,POST,TRACE
			.asax,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.ascx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.ashx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.asmx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.asp,C:\WINDOWS\system32\inetsrv\asp.dll,5,GET,HEAD,POST,TRACE
			.aspx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.axd,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.cdx,C:\WINDOWS\system32\inetsrv\asp.dll,5,GET,HEAD,POST,TRACE
			.cer,C:\WINDOWS\system32\inetsrv\asp.dll,5,GET,HEAD,POST,TRACE
			.config,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.cs,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.csproj,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.idc,C:\WINDOWS\system32\inetsrv\httpodbc.dll,5,GET,POST
			.licx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.rem,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.resources,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.resx,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.shtm,C:\WINDOWS\system32\inetsrv\ssinc.dll,5,GET,POST
			.shtml,C:\WINDOWS\system32\inetsrv\ssinc.dll,5,GET,POST
			.soap,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.stm,C:\WINDOWS\system32\inetsrv\ssinc.dll,5,GET,POST
			.vb,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.vbproj,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG
			.vsdisco,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,1,GET,HEAD,POST,DEBUG
			.webinfo,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,5,GET,HEAD,POST,DEBUG"
		WAMUserName="IWAM_DESTINATION"
		WAMUserPass="4963446270000000220000004000000068e601bbb4cd522a30c1ca97ae55868624ec7c6aec49da59aac18be039b5b0fc195649004e0044003efa28484ba3debde850c532c04d1fd358ac8a336aa43edd350be4a651de10b0012adadff0af6f380669ca5a86da004d61ed65ac4c2d8bfda776313e37d30109"
		WebSvcExtRestrictionList="1,*.dll
			1,*.exe
			1,C:\WINDOWS\system32\inetsrv\ssinc.dll,0,SSINC,Server Side Includes
			1,C:\WINDOWS\system32\bitssrv.dll,0,BITSEXTS,BITS Server Extensions
			1,C:\WINDOWS\system32\inetsrv\asp.dll,0,ASP,Active Server Pages
			1,C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\aspnet_isapi.dll,0,ASP.NET v1.1.4322,ASP.NET v1.1.4322
			1,C:\WINDOWS\system32\inetsrv\httpodbc.dll,0,HTTPODBC,Internet Data Connector
			1,C:\PHP\Distributions\php-5.0.4-Win32\php5isapi.dll,1,,PHP
			0,C:\WINDOWS\system32\inetsrv\httpext.dll,0,WEBDAV,WebDAV
			1,C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\isapi\_vti_aut\author.dll,0,Windows SharePoint Services,Windows SharePoint Services
			1,C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\isapi\_vti_adm\admin.dll,0,Windows SharePoint Services,Windows SharePoint Services
			1,C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\isapi\shtml.dll,0,Windows SharePoint Services,Windows SharePoint Services
			1,C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\isapi\owssvr.dll,0,Windows SharePoint Services,Windows SharePoint Services
			1,C:\Program Files\Common Files\microsoft shared\web server extensions\50\isapi\fpcount.exe,0,FPSE,FrontPage Server Extensions
			1,C:\Program Files\Common Files\microsoft shared\web server extensions\50\isapi\shtml.dll,0,FPSE,FrontPage Server Extensions
			1,C:\Program Files\Common Files\microsoft shared\web server extensions\50\isapi\_vti_adm\admin.dll,0,FPSE,FrontPage Server Extensions
			1,C:\Program Files\Common Files\microsoft shared\web server extensions\50\isapi\_vti_aut\author.dll,0,FPSE,FrontPage Server Extensions
			1,C:\Program Files\Common Files\microsoft shared\web server extensions\50\isapi\_vti_adm\fpadmdll.dll,0,FPSE,FrontPage Server Extensions"
	>