When you try to access a class from another class which have higher accessibility.
using System;
namespace MyApp
{
    public class Inconsistent_accessibility_Class
    {
        public static void Main(string[] args)
        {           
        }  
        public class_type my_prop
        {
            get
            {
                return new class_type();
            }
        }  
    }
    class class_type
    {
    }
}  
How to fix above Error:
add public access in front of class_type class.
 
using System;
namespace MyApp
{
    public class Inconsistent_accessibility_Class
    {
        public static void Main(string[] args)
        {           
        }  
        public class_type my_prop
        {
            get
            {
                return new class_type();
            }
        }  
    }
    public class class_type
    {
    }
}