Error inconsistent accessibility method C# -

get message:

"error 1 inconsistent accessibility: parameter type 'assignment_5.address' less accessible method 'assignment_5.contactmanager.addcontact(string, string, assignment_5.address)' c:\users\oscarisacson\documents\visual studio 2012\projects\assignment 5\assignment 5\contactfiles\contactmanager.cs 24 21 assignment 5 "

this method code(all classes public):

    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;     } 

and address class:

namespace assignment_5 {     public class address     {         private string m_street;         private string m_zipcode;         private string m_city;         private countries m_country;          public address() : (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>         /// function deletes "_" country names saves in enum.         /// </summary>         /// <returns>the country name whitout underscore char.</returns>         public string getcountrystring()         {             string strcountry = m_country.tostring();             strcountry = strcountry.replace("_", " ");             return strcountry;         }          /// <summary>         /// method overrides tostring method         /// </summary>         /// <returns>formatted string address detail on 1 line</returns>         public override string tostring()         {             return string.format("{0, -25} {1,-8} {2, -10} {3}", m_street, m_zipcode, m_city, getcountrystring());         }      } } 

the address class either protected, private or internal error. note classes internal default in c#.