Silverlight Random Fetch Error

I have a created a Read Only Lists that inherits from CSLA ReadOnlyListBase. I am calling a BeginGet method passing in a criteria class (both classes have been marked as serializable).

This fetch does work on the first call, however any subsequent calls of the same method are causing the error below:

ERROR MESSAGE:

{: at System.ServiceModel.AsyncResult.End[TAsyncResult](IAsyncResult result) at System.ServiceModel.Channels.ServiceChannel.EndCall(String action, Object[] outs, IAsyncResult result) at System.ServiceModel.ClientBase1.ChannelBase1.EndInvoke(String methodName, Object[] args, IAsyncResult result) at Csla.WcfPortal.WcfPortalClient.WcfPortalClientChannel.EndFetch(IAsyncResult result) at Csla.WcfPortal.WcfPortalClient.Csla.WcfPortal.IWcfPortal.EndFetch(IAsyncResult result) at Csla.WcfPortal.WcfPortalClient.OnEndFetch(IAsyncResult result) at System.ServiceModel.ClientBase`1.OnAsyncCallCompleted(IAsyncResult result) : Error HRESULT E_FAIL has been returned from a call to a COM component. at System.Net.Browser.BrowserHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult) at System.Net.Browser.BrowserHttpWebRequest.<>c_DisplayClassa.b_9(Object sendState) at System.Net.Browser.AsyncHelper.<>c_DisplayClass4.b_0(Object sendState) }

My breakpoint on the DataPortal_Fetch method is not being hit (after the first fetch) on the server side, as the error indicates. 

Any advice to help me solve this would be appreciated.