ModelState.IsValid == false, why?

About "can it be that 0 errors and IsValid == false": here's MVC source code from https://github.com/Microsoft/referencesource/blob/master/System.Web/ModelBinding/ModelStateDictionary.cs#L37-L41

public bool IsValid {
    get {
        return Values.All(modelState => modelState.Errors.Count == 0);
    }
}

Now, it looks like it can't be. Well, that's for ASP.NET MVC v1.

Paste the below code in the ActionResult of your controller and place the debugger at this point.

var errors = ModelState
    .Where(x => x.Value.Errors.Count > 0)
    .Select(x => new { x.Key, x.Value.Errors })
    .ToArray();

As you are probably programming in Visual studio you'd better take advantage of the possibility of using breakpoints for such easy debugging steps (getting an idea what the problem is as in your case). Just place them just in front / at the place where you check ModelState.isValid and hover over the ModelState. Now you can easily browse through all the values inside and see what error causes the isvalid return false.

bool hasErrors =  ViewData.ModelState.Values.Any(x => x.Errors.Count > 1);

or iterate with

    foreach (ModelState state in ViewData.ModelState.Values.Where(x => x.Errors.Count > 0))
    {

    }