I would create an Error view and then do something like this if you are expecting an error:
if(model == null)
{
ViewBag.Error = "Your x is not present, please try again later or contact xxx";
return View("Error");
}
On your error view then just check if ViewBag.Error
is present. (Error view should be in shared views).
Note I would only do this when you are excepting it to happen and you then can inform the users what they have done wrong. e.g. Editing something, you could return them this view and give them some more information to what they have done wrong.