http://support.microsoft.com/default.aspx?scid=kb;en-us;819267
INFO: HTTP GET and HTTP POST Are Disabled by Default
HTTP GET and HTTP POST may be enabled by editing the Web.config file for the
vroot where the Web service resides. The following configuration enables
both HTTP GET and HTTP POST:
<configuration>
<system.web>
<webServices>
<protocols>
<add name="HttpGet"/>
<add name="HttpPost"/>
</protocols>
</webServices>
</system.web>
</configuration>Alternatively, you can enable these protocols for all Web
services on the computer by editing the <protocols> section in
Machine.config. The following example enables HTTP GET, HTTP POST, and also
SOAP and HTTP POST from localhost:
<protocols>
<add name="HttpSoap"/>
<add name="HttpPost"/>
<add name="HttpGet"/>
<add name="HttpPostLocalhost"/>
<!-- Documentation enables the documentation/test pages -->
<add name="Documentation"/>
</protocols>