Silverlight IsolatedFileStorage Delete Directory

Basically, I am caching data while the application is running to improve performance but if the application is reloaded I want the application to cache everything again.  I currently have methods for caching the information to a file, reading it back in, or going to my web service to retrieve the information.  The logic for this code is:

IF cache file exists THEN
     Load Data From Cache
ELSE
     Retrieve data from Web Service
     Cache Data
END IF

With this in mind I thought the perfect way of clearing the cache would be to add code to the Application_Startup event in the App.xaml file to delete everything in the isolated file storage before the application ties to load.  I tried to accomplish with the following code:

    Private Shared Sub ClearDirectory(ByVal Directory As String)
        Dim isoStore As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication
        If isoStore.DirectoryExists(Directory) Then
            isoStore.DeleteDirectory(Directory)
        End If
    End Sub

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This code returns:

{System.IO.IsolatedStorage.IsolatedStorageException: Unable to create directory.
   at System.IO.IsolatedStorage.IsolatedStorageFile.DeleteDirectory(String dir)
   at ExecuKeysSL.Helper.FileManager.ClearDirectory(String Directory)
   ...........
}

I am unsure why I am getting an "Unable to create directory" error when I am trying to delete a directory.  I also checked to see what existed in isoStore.GetDirectoryNames:

?isostore.GetDirectoryNames
{Length=1}
    (0): "EKData"

Also note that I am running a test to verify that the directory exists before the line of code to delete the directory is run.

Ok, so I figured I would try to work around this issue with the following code:

    Private Shared Sub ClearDirectory(ByVal Directory As String)
        Dim isoStore As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication
        If isoStore.DirectoryExists(Directory) Then
            Dim files As String() = isoStore.GetFileNames(Directory & "*")
            For Each File In files
                isoStore.DeleteFile(File)
            Next
        End If
    End Sub

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The problem with this code is that isoStore.GetFileNames(Directory & "*") doesn't return any files even though they exist.  I even tried to see what was returned if I just asked for all of the files:

?isostore.GetFileNames("*")
{Length=0}

The last thing that I tried was to run isoStore.Remove which ran successfully.  The problem with running isoStore.Remove though is that eventually I am planning on storing additional information here besides cached results.  When I do I will not want this information deleted.

Any help that can be provided in resolving this would be greatly appreciated.