Websphere ESB 6.1 does not support Soap 1.2 yet. Presense of Soap1.2 bindings in .NET auto generated WSDL files created lots of problems with the new WID 6.1.2 release. So there are two options either modify WSDL manualy when importing to ESB or modify the .NET web service to supress Soap1.2.
To disable Soap1.2 binding generation add in web.config under <system.web>
<webServices>
<protocols>
<clear/>
<add name=“HttpSoap“ />
<add name=“Documentation“/>
</protocols>
</webServices>