E-Filing - Employee_tax_code_update - Channel Error

I am setting up the above scenario in PI 7.31 system

and setting up the four communication channels: - Logon, GetMessageBox, GetMessageDetail, DeleteMessage.

When I ping channel I get a not very helpful message: System Has Some Error

For example settings on communication channel - GetMessageBox

Target URL: - https://secure.gateway.gov.uk/ggmssoap/GGMSAPI.WSDL

SOAP Action: http://tempuri.org/action/SecureMailAPI.GetMessageBox

Configure proxy has been selected with proxy server and port.

I presume no other parameters need setting

Any ideas on what the error is?