Error with entering records in SQL Table using ASP.NET MVC

Hello,

I am getting the following error when attempting to add more than one record to a table.

System.Data.SqlClient.SqlException: 'Violation of PRIMARY KEY constraint 'PK__AOP6__3214EC075FC67488'. Cannot insert duplicate key in object 'dbo.AOP6'. The duplicate key value is (0).
The statement has been terminated.'

Any ideas what is causing this error?

I am using ASP.NET MVC.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Dapper;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

namespace DataLibrary.DataAccess
{
    public static class SqlDataAccess
    {
        public static string GetConnectionString(string connectionName = "MVCDemoDB")
        {
            return ConfigurationManager.ConnectionStrings[connectionName].ConnectionString;
        }

        public static List<T> LoadData<T>(string sql)
        {
            using (IDbConnection cnn = new SqlConnection(GetConnectionString()))
            {
                return cnn.Query<T>(sql).ToList();
            }
        }

        public static int SaveData<T>(string sql, T data)
        {
            using (IDbConnection cnn = new SqlConnection(GetConnectionString()))
            {
                return cnn.Execute(sql, data); *****ERROR Line*****
            }
        }
    }
}



Thanks,

Victor