I am getting an error calling a soap service, which I did not expect. The service does not require authentication or certificates, but I receive the following error:

An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll

Additional information: The client certificate is not provided. Specify a client certificate in ClientCredentials.

If I test the soap service in SoapUI it works just by loading the SVC and sending the request XML. So I expected this to work in C# just by calling the service, without certificate?