background transfer count windows phone
===

I'm to download files using Background Transfer Service for WP7 but the problem is sometimes my app crash for still unknown reasons for me and when i try to launch it again it just crash again with the following error.

> System.UriFormatException was unhandled   Message=Invalid URI: The
> format of the URI could not be determined.   StackTrace:    at
> System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind)
> at System.Uri..ctor(String uriString)    at
> Microsoft.Phone.BackgroundTransfer.BtsApi.QueryBackgroundTransferRequestTransferParameters(BtsRequestHandle
> requestHandle)    at
> Microsoft.Phone.BackgroundTransfer.BackgroundTransferRequest..ctor(BtsRequestHandle
> requestHandle, String requestId, RequestStatus requestStatus)    at
> Microsoft.Phone.BackgroundTransfer.BackgroundTransferService.BackgroundTransferRequestsEnumerator.MoveNext()
> at Transffr.MainPage.InitialTansferStatusCheck()    at
> Transffr.MainPage.OnNavigatedTo(NavigationEventArgs e)    at
> Microsoft.Phone.Controls.PhoneApplicationPage.InternalOnNavigatedTo(NavigationEventArgs
> e)    at
> System.Windows.Navigation.NavigationService.RaiseNavigated(Object
> content, Uri uri, NavigationMode mode, Boolean isNavigationInitiator,
> PhoneApplicationPage existingContentPage, PhoneApplicationPage
> newContentPage)    at
> System.Windows.Navigation.NavigationService.CompleteNavigation(DependencyObject
> content, NavigationMode mode)    at
> System.Windows.Navigation.NavigationService.ContentLoader_BeginLoad_Callback(IAsyncResult
> result)    at
> System.Windows.Navigation.PageResourceContentLoader.BeginLoad_OnUIThread(AsyncCallback
> userCallback, PageResourceContentLoaderAsyncResult result)    at
> System.Windows.Navigation.PageResourceContentLoader.<>c__DisplayClass4.<BeginLoad>b__0(Object
> args)    at
> System.Reflection.RuntimeMethodInfo.InternalInvoke(RuntimeMethodInfo
> rtmi, Object obj, BindingFlags invokeAttr, Binder binder, Object
> parameters, CultureInfo culture, Boolean isBinderDefault, Assembly
> caller, Boolean verifyAccess, StackCrawlMark& stackMark)    at
> System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj,
> BindingFlags invokeAttr, Binder binder, Object[] parameters,
> CultureInfo culture, StackCrawlMark& stackMark)    at
> System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)  
> at System.Delegate.DynamicInvokeOne(Object[] args)    at
> System.MulticastDelegate.DynamicInvokeImpl(Object[] args)    at
> System.Delegate.DynamicInvoke(Object[] args)    at
> System.Windows.Threading.DispatcherOperation.Invoke()    at
> System.Windows.Threading.Dispatcher.Dispatch(DispatcherPriority
> priority)    at System.Windows.Threading.Dispatcher.OnInvoke(Object
> context)    at System.Windows.Hosting.CallbackCookie.Invoke(Object[]
> args)    at
> System.Windows.Hosting.DelegateWrapper.InternalInvoke(Object[] args)  
> at System.Windows.RuntimeHost.ManagedHost.InvokeDelegate(IntPtr
> pHandle, Int32 nParamCount, ScriptParam[] pParams, ScriptParam&
> pResult)

which i don't understand because is in this line of code:

    if (TransferListBox.Items.Count > 0)
    {
       //Some code here
    }

And i'm trying to count list items why does it tells me invalid URI?

And always crash using a valid Absolute URL.

Thanks for any help.