MVC5 / C# – Cannot perform runtime binding on a null reference

There are two issues in your code:
Consider this:
public ActionResult Index()
{
int n = 0;
ViewBag.speakers[n] = 5;
return View();
}

This simplified piece of code throws Cannot perform runtime binding on a null reference since speakers is not defined (null reference).
You can fix it by defining speakers in the dynamic ViewBag before the loop:
ViewBag.speakers = new List();

The second issue:
ViewBag.speakers[n] = speakers;

speakers in your code is a List, you might want to define ViewBag.speakers as a List> and call .Add(speakers) instead of accessing using an index (you might get index was out of range)

Calling the .ToString() method on a null column value can result in the Cannot perform runtime binding on a null reference. Use Convert.ToString() instead; it will return an empty string if you attempt to convert a null value and won’t require additional code for null checking.