Simple silverlight open-file-dialog errors

Question

A while back I wrote a silverlight user control which had a csv import/export feature. This has been working fine, until recently I discovered it erroring in one scenario. This may have been due to moving to Silverlight 3.

The Error:
Message: Unhandled Error in Silverlight 2 Application
Code: 4004
Category: ManagedRuntimeError
Message: System.Security.SecurityException: Dialogs must be user-initiated.
       at System.Windows.Controls.OpenFileDialog.ShowDialog()
       at MyControl.OpenImportFileDialog()
       at ...

The Code:

private void BrowseFileButton_Click(object sender, RoutedEventArgs e)
{
    if (string.IsNullOrEmpty(lblFileName.Text))
    {
        if (MessageBox.Show("Are you sure you want to change the Import file?", "Import", MessageBoxButton.OKCancel) == MessageBoxResult.Cancel)
        {
            return;
        }
    }
    EnableDisableImportButtons(false);
    var fileName = OpenImportFileDialog();
    lblFileName.Text = fileName ?? string.Empty;
    EnableDisableImportButtons(true);    
}

private string OpenImportFileDialog()
{
    var dlg = new OpenFileDialog { Filter = "CSV Files (*.csv)|*.csv" };
    if (dlg.ShowDialog() ?? false)
    {
        using (var reader = dlg.File.OpenText())
        {
            string fileName;
            //process the file here and store fileName in variable
            return fileName;
        }
    }
}

I can open an import file, but if i want to change the import file, and re-open the file dialog, it errors. Does anyone know why this is the case?
Also, I am having trouble debugging because placing a breakpoint on the same line (or prior) to the dlg.ShowDialog() call seems to cause this error to appear as well. Any help would be appreciated?

Solution

You do two actions on one user click.

You show a messagebox which effectively uses your permission to show a dialog on user action.

You then try to show the dialog, since this is a second dialog on user action it's not allowed.

Get rid of the confirmation dialog and you'll be fine.