Database forign key error

public partial class UploadedFile : System.Web.UI.Page
{
SqlConnection con = new SqlConnection("Data Source=cook;Initial Catalog=MIS;Integrated Security=True");
protected void Page_Load(object sender, EventArgs e)
{

}

private void StartUpLoad()
{
//get the file name of the posted image
string fileName = FileUpload1.FileName.ToString();

//now we will set the image path
string filePath = "ImageStorage/" + fileName;

//then save it to the folder
FileUpload1.SaveAs(Server.MapPath(filePath));

//now get the size in bytes of the file
//int fileSize = FileUpload1.PostedFile.ContentLength;

//validate the posted file before saving

if (FileUpload1.PostedFile != null && FileUpload1.FileName != "")
{
if (FileUpload1.PostedFile.ContentLength > 8120)
{
Page.ClientScript.RegisterClientScriptBlock(typeof(Page), "Alert", "alert('File is too big')", true);
}
else
{
//save the file
//call the method to execute insertion of data to the database
ExecuteInsert(filePath);
Label.Text = "File" + fileName + "Successfully uploaded";

}
}

}

private string GetConnectionString()
{
//sets the connection string from web.config
return
System.Configuration.ConfigurationManager.ConnectionStrings["MyDataEntries"].ConnectionString;
}

private void ExecuteInsert(string path)
{
SqlConnection conn = new SqlConnection(GetConnectionString());

string sql = "INSERT INTO JobPortalDatabase (FirstName,LastName,StreetAddress,EmailAddress,ContactNumber,PositionAppliedFor,NameoftheCompany,AddressofCompany,NameofSupervisor,EnterContactNumberofSupervisor,EmailAddressofSupervisor,DescribeYourDuties,NameoftheCompany1,AddressofCompany1,NameofSupervisor1,EnterContactNumberofSupervisor1,EmailAddressofSupervisor1,DescribeYourDuties1,FilePath,FileName) VALUES ('" + TextBox1.Text + "' , '" + TextBox2.Text + "' , '" + TextBox3.Text + "' , '" + TextBox4.Text + "' , '" + TextBox5.Text + "' , '" + TextBox6.Text + "' , '" + TextBox7.Text + "' , '" + TextBox8.Text + "' , '" + TextBox9.Text + "' , '" + TextBox10.Text + "' , '" + TextBox11.Text + "' , '" + TextBox12.Text + "' , '" + TextBox13.Text + "' , '" + TextBox14.Text + "' , '" + TextBox15.Text + "' , '" + TextBox16.Text + "' , '" + TextBox17.Text + "' , '" + TextBox18.Text + "' , '" + FileUpload1+ "' , '" + FileUpload1.FileName + "')";

try
{
conn.Open();

SqlCommand cmd = new SqlCommand(sql, conn);

//SqlParameter[] param = new SqlParameter[2];

//param[0] = new SqlParameter("@FilePath", SqlDbType.VarChar, 50);

//param[0].Value = path;

//for (int i = 0; i < param.Length; i++)
//{
// cmd.Parameters.Add(param[i]);
//}
cmd.CommandType = CommandType.Text;
cmd.ExecuteNonQuery();
}

catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Insert error";
msg += ex.Message;
throw new Exception(msg);
}

finally
{
conn.Close();

}

}
protected void Button2_Click(object sender, EventArgs e)
{
StartUpLoad();

}
protected void Button3_Click(object sender, EventArgs e)
{

Response.Redirect("PersonalInformation.aspx");
}
}