AX 2012 Query Service - Log on error

I'm brand new to AX 2012.  I'm a web developer and I use ASP.Net. 

I am trying to use the AX 2012 query service to fetch a dataset from AX 2012.  So I added the service reference to my ASP.Net web site.  This seemed to work ok.  I then logged an using the Active DIrectory user log on.  It seemed to let me log on correctly.  I wrote this code to try to get a dataset:

QueryServiceClient client = new QueryServiceClient();       
Paging paging = null;

DataSet ds = client.ExecuteStaticQuery("CustTable", ref paging);
gvCust.DataSource = ds;
gvCust.DataBind();

I get the following error on this line: DataSet ds = client.ExecuteStaticQuery("CustTable", ref paging);

Unable to log on to Microsoft Dynamics AX

I have done several searches online and can't seem to find anything.  WHat am I doing wrong?