错误不一致的可访问性方法C#

获取消息：

"错误1可访问性不一致：参数类型'Assignment_5.Address'的可访问性不如方法'Assignent_5.ContactManager.AddContact（string，string，Assignment_5.Access）'C:''Users''OscarIsacson''documents''visual studio 2012''Projects''Assignment 5''Assignment 5''ContactFiles''ContactManager.cs 24 21 Assignment 5"

这是方法代码（所有类都是公共的）：

    private List<Contact> m_contactRegistry;
    public bool AddContact(string firstName, string lastName, Address adressIn) 
    {
        Contact contactIn = new Contact(firstName, lastName, adressIn);
        m_contactRegistry.Add(contactIn);
        return true;
    }
    public bool AddContact(Contact ContactIn)
    {
        m_contactRegistry.Add(ContactIn);
        return true;
    }

地址类别：

namespace Assignment_5
{
    public class Address
    {
        private string m_street;
        private string m_zipCode;
        private string m_city;
        private Countries m_country;
        public Address() : this (string.Empty, string.Empty, "Göteborg")
        {
        }
        public Address(string street, string zip, string city)
            : this(street, zip, city, Countries.Sweden)
        { 
        }
        public Address(string street, string zip, string city, Countries country)
        {
        }
        public string Street;
        public string City;
        public string ZipCode;
        public Countries Country;
        /// <summary>
        /// This function simply deletes the "_" from country names as saves in the enum.
        /// </summary>
        /// <returns>the country name whitout the underscore char.</returns>
        public string GetCountryString()
        {
            string strCountry = m_country.ToString();
            strCountry = strCountry.Replace("_", " ");
            return strCountry;
        }
        /// <summary>
        /// Method that overrides the ToString method
        /// </summary>
        /// <returns>Formatted string with address detail on one line</returns>
        public override string ToString()
        {
            return string.Format("{0, -25} {1,-8} {2, -10} {3}", m_street, m_zipCode, m_city, GetCountryString());
        }
    }
}