>AH HA! When you added the constructor, .Net wants to use it everytime. However, when it's created here, there is no constructor that takes no parameters. Create one, and things should start working.
>
I've created one and I am back to my original problem (I think). I am now hitting the Edit method again, but the IsValid comes as false for the model.

So, something is still not right :(

Ok, the weird thing is - this is the error

"The field Ext must be a string with a maximum length of 5."

That's weird - should not it still let the extension be nothing?

Here is how my Client is defined:

using System;

using System.ComponentModel.DataAnnotations;
using System.ComponentModel;

using DataAnnotationsExtensions;
using System.ComponentModel.DataAnnotations.Schema;
using System.Collections.Generic;

namespace CardNumbers.Objects
{
    [ComplexType]
    public class PhoneInfo
    {
        [DataType(DataType.PhoneNumber)]
        
        [DisplayName("Phone")]
        [RegularExpression(@"^((\(\d{3}\)|\d{3})\s?)?\d{3}[-\s]?\d{4}\s*$", ErrorMessage = "Please enter valid Phone Number")]
        public virtual string Phone { get; set; }

        [StringLength(5)]
        [DisplayName("Ext")]
        public virtual string Ext { get; set; }

        public bool HasValue
        {
            get
            {
                return (Phone != null || Ext != null);
            }
        }

    }

      [ComplexType]
      public class ContactDetail
      {
          //Constructor
          public ContactDetail()
          {
              phoneInfo = new PhoneInfo();
          }

          [StringLength(100)]
          [DisplayName("Contact Name")]
          [DisplayFormat(NullDisplayText = "")]
          public virtual string Contact { get; set; }

          [Email]
          [StringLength(100)]
          [DataType(DataType.EmailAddress)]
          [DisplayName("Email")]
          public virtual string Email { get; set; }

          public virtual PhoneInfo phoneInfo { get; set; }
          public bool HasValue
          {
              get
              {
                  return (Contact != null || Email != null || phoneInfo.HasValue);
              }
          }
      }

/// <summary>
/// Client class (Client No, Client Name, Address, Contact1, Contact2 info, Created By, Modified By (operator and date)
/// </summary>
    public class Client
    {
        public Client()
        {
            Contact1 = new ContactDetail();
            Contact2 = new ContactDetail();
     }

        [Key]
        [Editable(false)]
        [Column("ClientId",TypeName = "int")]
        public virtual int Id { get; set; }
        
        //[Required]
        [DisplayName("Client No")]      
        [Column("client_no", TypeName = "smallint")]
        public virtual Int16 Number { get; set; }
        
        //[Required]
        [Column("client_name", TypeName = "varchar")]
        [DisplayName("Client Name")]
        [MaxLength(30, ErrorMessage = "Client Name should not be longer than 30 characters" )]
        [MinLength(3, ErrorMessage = "Client Name is too short")]

        public virtual string Name { get; set; }

        [DataType(DataType.MultilineText)]
        public virtual string Address { get; set; }

        public virtual ContactDetail Contact1 {get; set;}
        public virtual ContactDetail Contact2 {get; set;}

        [ForeignKey("EnteredByOperator")]
        public string EnteredBy { get; set; }

        [InverseProperty("ClientsEnteredBy")]
        public virtual Operator EnteredByOperator { get; set; }

        [ForeignKey("ModifiedByOperator")]
        public string ModifiedBy { get; set; }

        [InverseProperty("ClientsUpdatedBy")]
        public virtual Operator ModifiedByOperator { get; set; }

        [DataType(DataType.DateTime)]
        [DisplayName("Created on")]
        public DateTime EnteredOn { get; set; }

        [DataType(DataType.DateTime)]
        [DisplayName("Modified on")]
        public DateTime? ModifiedOn { get; set; }

        public virtual ICollection<ClientOrder> ClientOrders { get; set; }
        
        public virtual ICollection<Reorder> Reorders { get; set; }
    }
}

So, I don't even put anything in the Extension box, why does it produce the error?