When trying to connect to eXist with SOAP from .NET, Jes tells me he and Manu use the following successfully:
QueryService service = new QueryService();
sessionId = service.connect(userName, password);
When I try this, I get:
An unhandled exception of type 'System.NET.WebException' occurred in system.web.services.dll
Additional information: The request failed with HTTP status 405: Method not allowed.

The developer documentation for eXist says the connection sequence should look something like:
QueryService service = new QueryServiceLocator();
Query query = service.getQuery();
String session = query.connect("guest", "guest");
This always results in an error that says QueryServiceLocator doesn't even exist in the namespace.