Error when in Silverlight when trying to reach an RIA Services endpoint

I created a Ria services endpoint. Silverlight passes data into the RIA Services. The end point then writes/updates this data to the file system. We are experiencing the following exception:

System.ServiceModel.DomainServices.Client.DomainOperationException: Invoke operation 'Modi开发者_开发百科fyLogiDashletXmlFile' failed. Exception of type 'System.ServiceModel.DomainServices.Client.DomainOperationException' was thrown. at Phoenix.UI.SL.Infrastructure.Services.LogiReportService.<>c_DisplayClass8.<ModifyLogiDashletXmlFile>b_7(InvokeOperation operation) at System.ServiceModel.DomainServices.Client.InvokeOperation.<>c_DisplayClass41.<Create>b__0(InvokeOperation1 arg) at System.ServiceModel.DomainServices.Client.InvokeOperation`1.InvokeCompleteAction() at System.ServiceModel.DomainServices.Client.OperationBase.Complete(Exception error) at System.ServiceModel.DomainServices.Client.InvokeOperation.Complete(Exception error) at System.ServiceModel.DomainServices.Client.DomainContext.CompleteInvoke(IAsyncResult asyncResult) at System.ServiceModel.DomainServices.Client.DomainContext.<>c_DisplayClass38.<InvokeOperation>b__34(Object )

the attributes on the class:

[EnableClientAccess(RequiresSecureEndpoint = true)]
    [LinqToEntitiesDomainServiceDescriptionProvider(typeof(PhoenixEntities))] // IMPORTANT: Must have this because we are returning/passing EF Entities from Phoenix Context
    [RequiresAuthentication]
    public class LogiReportService : DomainService
    {
...

}

The entry method:

[Invoke]
public void ModifyLogiDashletXmlFile(IEnumerable<ParameterNameValuePair> paramNameValuePairs, Guid clientId, string dashletInstanceId)
{

    // Validate Client is has a valid relationship to the User (i.e. no disabled)
    if (this.PhoenixUser.MembershipClientIds.Contains(clientId))
    {
       ModifyLogiXmlFile(PhoenixUser.UserId, clientId.ToString(), dashletInstanceId, paramNameValuePairs);
    }
}

What's baffling is other endpoints work fine. The differences between this endpoint and the other is this one writes and reads files from the file-system. The app-domain user has full-rights and the error returned does not appear to be a permissions issue.

All idea's are welcomed. I'm hitting up against a wall with this issue.

This issue turned out to be a permissions issue on the server. A file was being written to the system.

RIA services was swallowing the error and presenting a generic error in it's stead. I put a try catch around the entry method and logged the error to the database. Then I was able to discover the real issue.