@Html.TextBoxFor(model => model.CreationDate, new { @class = "form-control datepicker", @Value = DateTime.Now.ToString("dd'/'M'/'yyyy"), type = "datetime" })

<input value="31/3/2014" class="form-control datepicker" data-val="true" data-val-date="The field CreationDate must be a date." data-val-required="Data jest wymagana" id="CreationDate" name="CreationDate" type="datetime">

The value "31/3/2014" is not valid for CreationDate.

+       CreationDate    {0001-01-01 00:00:00}   System.DateTime

$('.datepicker').datepicker({
        format: "dd/MM/yyyy",
        language: "pl",
        autoclose: true,
        todayHighlight: true
    });

"31/Marzec/2014"

public class CreateDeviceInstance
{
    public int Id { get; set; }
    public int DeviceId { get; set; }
    public string SerialNo { get; set; }
    [Required(ErrorMessage="Data jest wymagana")]
    public System.DateTime CreationDate { get; set; }
    public Nullable<int> ProjectId { get; set; }
    public bool Issue { get; set; }
    public string IssueDetails { get; set; }
    public Nullable<int> StorageId { get; set; }
    public bool MeAsUser { get; set; }
}

(DateTime.Now.ToString("dd'/'M'/'yyyy"))

format: "dd/MM/yyyy"

public int Id { get; set; }
public int DeviceId { get; set; }
public string SerialNo { get; set; }
[Required(ErrorMessage="Data jest wymagana")]
[DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
public System.DateTime CreationDate { get; set; }
public Nullable<int> ProjectId { get; set; }
public bool Issue { get; set; }
public string IssueDetails { get; set; }
public Nullable<int> StorageId { get; set; }
public bool MeAsUser { get; set; }