InvalidCastException from windows phone 7 talking to a .asmx web service

Question

I have a .NET 2.0 .asmx web service that looks something like this:

[WebMethod]
[return: XmlArray("FileInformations"), XmlArrayItem("FileInformation")]
public FileInformation[] GetFileInformation(
        [XmlElement("Path")] string path)

When I try to call this web service from a silverlight windows phone 7 app (beta). I get an InvalidOperationException with an inner InvalidCastException but no further details.

This same service works perfectly when called by a desktop WCF client.

The silverlight proxy generated looks like this:

[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "4.0.0.0")]
[System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Advanced)]
[System.ServiceModel.MessageContractAttribute(WrapperName="GetFileInformationResponse", WrapperNamespace="http://example.com", IsWrapped=true)]
public partial class GetFileInformation {

    [System.ServiceModel.MessageBodyMemberAttribute(Namespace="http://example.com", Order=0)]
    [System.Xml.Serialization.XmlArrayItemAttribute("FileInformation")]
    public FileInformation[] FileInformation;

I noticed that it lacked an XmlArrayAttribute definition, but it didn't change anything even when I did add it explicitly.

For reference, the actual XML response looks like this:

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xmlns:xsd="http://www.w3.org/2001/XMLSchema"&gt;
 <soap:Body>
  <FileInformationResponse xmlns="http://example.com"&gt;
   <FileInformations>
    <FileInformation
     fileName="foo.txt" />
   </FileInformations>
  </GetFileInformations>
 </soap:Body>
</soap:Envelope>

What am I doing wrong?