Why is my code not CLS-compliant?

I've got errors when I build my project:

Warning as Error: Type of 'OthersAddresses.AddresseTypeParameter' is not CLS-compliant C:...\Units\OthersAddresses.ascx.cs

public Address.AddressTypeEnum AddressTypeParameter
    {
        get 
        {
            return _addressTypeParameter;
        }
        set 
        {
            _addressTypeParameter = value;
        }
    }

and this one:

Warning as Error: Type of 'Global.UserInSession' is not CLS-compliant C:...\Global.asax.cs

public static User UserInSession
{
    get
    {
        return (HttpContext.Current.Session["CurrentUser"] == null) 
            ? null 
            : HttpContext.Current.Session["CurrentUser"] as User;
    }
    set
    {
        HttpContext.Current.Session["CurrentUser"] = value;
    }
}

I added attribute [CLSCompliant(false)] before UserInSession and AddresseTypeParameter and it works but I would like to understand why it was not CLS-compliant.

Some more information about classes and enum:

Class User (User.cs)

public class User
    {
        private string _uniqueIdentifier;
        private string _password = string.Empty;
        private string _email = string.Empty;
        private string _passwordQuestion = string.Empty;
        private string _passwordAnswer = string.Empty;
        private string _id_directions_db = string.Empty;
        private string _id_gesab = string.Empty;
        private string _zipCode = string.Empty;
        private string _fonction_id = string.Empty;
        private string _fonction = string.Empty;
        private string _structure_id = string.Empty;
        private string _structure = string.Empty;
        private string _firstName = string.Empty;
        private string _lastName = string.Empty;
        private string _