Object that's passed in isn't recognized as an object?

using System;
using System.Collections.Generic;

class Program {
  public static void Main (string[] args) {
    List<Lot> auction = new List<Lot>();

    mainMenu(auction);
  }

  public void mainMenu(List<Lot> lots) {
    Lot currentLot = null;
    ...

  }
}

using System;
using System.Collections.Generic;

class Program {
  public static void Main (string[] args) {
    List<Lot> auction = new List<Lot>();

    mainMenu(auction);
  }

  public void mainMenu(List<Lot> lots) {
    Lot currentLot = null;
    ...

  }
}