Json反序列化错误

我得到这个错误，而试图反序列化JSON字符串对象:

    "System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> Newtonsoft.Json.JsonSerializationException: Error converting value "{"Admin":false,"Id":1,"Password":"heslo","Nick":"jozifek"}" to type 'Entities.dbo.User'. Path 'Frontman', line 1, position 105. ---> System.ArgumentException: Could not cast or convert from System.String to Entities.dbo.User.
   at Newtonsoft.Json.Utilities.ConvertUtils.EnsureTypeAssignable(Object value, Type initialType, Type targetType)
   at Newtonsoft.Json.Utilities.ConvertUtils.ConvertOrCast(Object initialValue, CultureInfo culture, Type targetType)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   --- End of inner exception stack trace ---
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type)
   at BussinessLogic.helpers.Serializer.Deserialize[T](String obj) in C:'Users'Ondra'documents'visual studio 2010'Projects'webServiceTestApp'BussinessLogic'helpers'Serializer.cs:line 14
   at webServiceTestApp.Service1.GetSongs(String band) in C:'Users'Ondra'documents'visual studio 2010'Projects'webServiceTestApp'webServiceTestApp'Service1.asmx.cs:line 142
   --- End of inner exception stack trace ---"

User.cs是这样的:

namespace Entities.dbo
{
    [TableName("tbl_user")]
    public class User : AbstractEntity
    {
        [MapField("nick")]
        public string Nick { get; set; }
        [MapField("password")]
        public string Password { get; set; }
        [MapField("admin")]
        public bool Admin { get; set; }
    }
}

和Band.cs是这样的:

namespace Entities.dbo
{
    [TableName("tbl_band")]
    public class Band : AbstractEntity
    {
        [MapField("name")]
        public string Name { get; set; }
        [MapField("frontman")]
        public int FrontmanId { get; set; }
        [Association(CanBeNull = false, ThisKey = "FrontmanId", OtherKey = "Id")]
        public User Frontman { get; set; }

AbstractEntity:

namespace Entities.helpers
{
    public abstract class AbstractEntity
    {
        [PrimaryKey, Identity, MapField("id")]
        public int Id { get; set; }
        public string Serialize()
        {
            return JsonConvert.SerializeObject(this);
        }
    }
}

和这个错误弹出当我发送字符串反序列化为乐队包含用户对象在Frontman属性..

你知道我哪里出错了吗?

谢谢:)