建立EF访问数据库架构时，出现One or more validation errors were detected during model generation

using System.ComponentModel.DataAnnotations.Schema;
using System.ComponentModel.DataAnnotations;
using System;
namespace Feng.Entity
{
    [Serializable]
    [Table("dict_sample")]
    public class Dict_sample
    {
        [Key]//必须要添加的特性，要和数据库主键对应
        [Column("sam_id")]
        [StringLength(12)]
        public string Sam_id
        { get; set; }

        [Column("sam_name")]
        [StringLength(50)]
        public string Sam_name
        { get; set; }

        [StringLength(18)]
        [Column("sam_code")]
        public string Sam_code
        { get; set; }

        [StringLength(12)]
        [Column("sam_incode")]
        public string Sam_incode
        { get; set; }

        [StringLength(12)]
        [Column("sam_type")]
        public string Sam_type
        { get; set; }

        [StringLength(18)]
        [Column("sam_py")]
        public string Sam_py
        { get; set; }

        [StringLength(18)]
        [Column("sam_wb")]
        public string Sam_wb
        { get; set; }

        [Column("sam_seq")]
        public int Sam_seq
        { get; set;
        }

        [StringLength(1)]
        [Column("sam_del")]
        public string Sam_del
        { get; set; }

        [StringLength(18)]
        [Column("sam_custom_type")]
        public string Sam_custom_type
        { get; set; }

        [StringLength(100)]
        [Column("sam_trans_code")]
        public string Sam_trans_code
        { get; set; }

    }
}