It looks like the OP is running from source code, which might be impacting the issue. However we could do more to catch the error for belt-and-braces.
Stack Trace: at System.Windows.Duration.get_TimeSpan() at XiboClient.Rendering.Video.MediaElement_MediaOpened(Object sender, RoutedEventArgs e) in C:\Users\User\Documents\Source\xibo-dotnetclient\Rendering\Video.cs:line 142
It looks like the OP is running from source code, which might be impacting the issue. However we could do more to catch the error for belt-and-braces.