SQL Server 2005 Reporting Serivces: XML Datasource Problem

Hi,

I'm just starting to use SQL Server 2005 Reporting services, and need to use an XMLdocument as the datasource. I will get the xml data from a webservice and then need to bind it to the report. Here is what I am doing:

1. I created a webservice at the following location:
http://localhost/myWebDirectory/myService.asmx. this webservice has a method called "GetXMLDocument" that has 1 parameter (sql). This method uses the sql statement to fill a dataset from a SQL Server database, converts it to an xmlDocument, and returns the xmlDocument. Here is a sample of the results:

<?xml version="1.0" encoding="utf-8" ?>
- <NewDataSet>
- <Table>
<ReportName>GirlsNamedMary</ReportName>
<ReportFriendlyName>All Girls Named Mary</ReportFriendlyName>
<ReportDescription>This is a test SQL Server Reporting Services report. It has no parameters.</ReportDescription>
</Table>
</NewDataSet>




2. I created a datasource in my reports project as follows:
- Name: TestDataSource
- Type: XML
- Connection string: http://localhost/myWebDirectory/myService.asmx

3. I created the following dataset:
- Name: TestDataSet
- Data source: TestDataSource
- Query string:
<Query xmlns="http://tempuri.org/Service/GetXMLDocument">
<Method Namespace="http://tempuri.org/Service" Name="GetXMLDocument"/>
<ElementPath />
</Query>

I am getting this error:
------------------------------------------------------------------------------------
An error occurred while executing the query. Failed to execute web request for the specified URL.

Additional Information:
----> Failed to execute web request for the specified URL. (Microsoft.ReportingServices.DataExtensions).
------------------------------------------------------------------------------------

I cannot figure out why I have this error. The service runs fine from the browser, but I just can't get it to work in Reporting Services. What am I doing wrong?