Jak stworzyc dodatek - poradnik

Message:
Client found response content type of 'text/html', but expected 'text/xml'.
The request failed with the error message:
--
Invalid query: Duplicate entry '' for key 2
--.

SimPE Version:
Default (0.52.2170.26328).

Exception Stack:
System.InvalidOperationException: Client found response content type of 'text/html', but expected 'text/xml'.
The request failed with the error message:
--
Invalid query: Duplicate entry '' for key 2
--.
at System.Web.Services.Protocols.SoapHttpClientProtoc ol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
at System.Web.Services.Protocols.SoapHttpClientProtoc ol.Invoke(String methodName, Object[] parameters)
at Sims.GUID.Service.SimGUIDService.registerUser(Stri ng username, String password)
at Sims.GUID.GUIDGetterForm.RegisterNewUser(Object sender, EventArgs e)

Source:
System.Web.Services

Execution Stack:
at System.Web.Services.Protocols.SoapHttpClientProtoc ol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
at System.Web.Services.Protocols.SoapHttpClientProtoc ol.Invoke(String methodName, Object[] parameters)
at Sims.GUID.Service.SimGUIDService.registerUser(Stri ng username, String password)
at Sims.GUID.GUIDGetterForm.RegisterNewUser(Object sender, EventArgs e)

- A czy ktoś umie wytłómaczyć dlaczego mam taki komunikat, gdy chcę się tam zarejestrować?