[Solved] Problem with K2 Filterservice

I must use the K2 filterservice il order to retrieve the process instance history. I've followed this article  http://kb.k2workflow.com/articles/kb000021.aspx but the sample project as my project fails with the error :

"Exception Page_Load : System.Net.WebException: La
demande a échoué avec l'état HTTP 401 : Unauthorized. à
System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage
message, WebResponse response, Stream responseStream, Boolean
asyncCall) à
System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String
methodName, Object[] parameters) à
localhost.FilterService.CreateSession(String ServerName, String
Connstr)"

Does somebody have a problem like this and, I hope, a solution.

Thanks.