A significant difference between all of these methods is that only the MouseClick method simulate a real user action. It is possible to get NullRefernceException if the element you're trying to click on is not currently presented on the screen. If this is the case, to overcome the issue try using the ScrollToVisible method before the MouseClick.
If you are experiencing something different a local reproduction is needed. Please provide the means to reproduce the issue locally(either in your app or on a public site), so we can try to determine what is causing the problem. Alternatively you can record a Fiddler trace using FiddlerCap
and send it to us in a zip file.
the Telerik team