Argument out of Range Exception using NavigationService

While not all the time, I am receiving an Argument out of range exception on a simple NavigationService call.

NavigationService.Navigate(New Uri("/MainPage.xaml", UriKind.Relative));

This works most of the time, but once in a while it fails and says the arguments aren't valid. If you notice. THERE ARE NO ARGUMENTS AT ALL TO FAIL. I'm guessing there is some other exception maybe? Not sure what it would be. I've looked on Google and around here and haven't seen a similar example. Any ideals appreciated.

Here is the stack trace.

System.Windows.dll!System.Windows.Threading.DispatcherTimer.Interval.set(System.TimeSpan value) + 0x10 bytes    
    Microsoft.Advertising.Mobile.UI.dll!Microsoft.Advertising.Mobile.UI.AdControl.PauseTimer() + 0x77 bytes 
    Microsoft.Advertising.Mobile.UI.dll!Microsoft.Advertising.Mobile.UI.AdControl.DeactivateAdControl() + 0x1d bytes    
    Microsoft.Advertising.Mobile.UI.dll!Microsoft.Advertising.Mobile.UI.AdControl.OnApplicationPageDeactivated(object sender, System.Window开发者_如何学Cs.Navigation.NavigatingCancelEventArgs e) + 0x39 bytes   
    Microsoft.Phone.dll!System.Windows.Navigation.NavigationService.RaiseNavigating(System.Uri uri, System.Windows.Navigation.NavigationMode mode, bool isFragmentNavigationOnly, Microsoft.Phone.Controls.PhoneApplicationPage existingContentPage) + 0x1c bytes   
    Microsoft.Phone.dll!System.Windows.Navigation.NavigationService.Navigate(System.Uri source) + 0x178 bytes   

I don't like the answer to this, but it looks like an AdControl defect. Below are mentions of this.

http://forums.create.msdn.com/forums/p/66644/473406.aspx http://community.microsoftadvertising.com/forums/p/68721/98240.aspx