SQL Server 2012 - ASP.NET - VB.NET - Einfügen von Daten in die Datenbank

Ich versuche, fügen Sie Daten zu einer db-Tabelle mithilfe von SQL-Anweisung mit VB.NET.

Dies ist mein code:

Registrierung.aspx:

Imports dbConnect
Imports System.Data.SqlClient


Partial Class Registration
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load

    End Sub

    Protected Sub btnRegister_Click(sender As Object, e As EventArgs) Handles btnRegister.Click

        register()


    End Sub


    Public Sub register()



        Dim Username As String = txtUsername.ToString
        Dim Surname As String = txtSurname.ToString
        Dim Password As String = txtPassword.ToString
        Dim Name As String = txtName.ToString
        Dim Address1 As String = txtAddress1.ToString
        Dim Address2 As String = txtAddress2.ToString
        Dim City As String = txtCity.ToString
        Dim Email As String = txtEmail.ToString
        Dim Country As String = drpCountry.ToString
        Dim DOB As Date = calDOB.SelectedDate
        Dim Occupation As String = txtOccupation.ToString
        Dim WorkLocation As String = txtWorkLocation.ToString
        Dim Age As Integer = "20"

        Dim ProjectManager As String = "test"
        Dim TeamLeader As String = "test"
        Dim TeamLeaderID As Integer = 1
        Dim ProjectManagerID As Integer = 1

        Dim RegistrationDate As Date = Today
        Dim ContractType As String = "test"
        Dim ContractDuration As Integer = 6
        Dim Department As String = "test"
        Dim conn As New SqlConnection("Data Source=BRIAN-PC\SQLEXPRESS;Initial Catalog=master_db;Integrated Security=True")
        Dim registerSQL As SqlCommand
        Dim sqlComm As String

        sqlComm = "INSERT INTO users(Username, Password, Name, Surname, Address1, Address2, City, Country, date_of_birth, age, Occupation, department, work_location, project_manager,team_leader, team_leader_id, project_manager_id, date_registration, contract_type, contract_duration) VALUES('" + Username + "','" + Password + "','" + Name + "','" + Surname + "','" + Address1 + "','" + Address2 + "','" + City + "','" + Country + "','" + DOB + "','" + Age + "','" + Occupation + "','" + Department + "','" + WorkLocation + "','" + ProjectManager + "','" + TeamLeader + "','" + TeamLeaderID + "','" + ProjectManager + "','" + RegistrationDate + "','" + ContractType + "','" + ContractDuration + "')"

        conn.Open()

        registerSQL = New SqlCommand(sqlComm, conn)

        registerSQL.ExecuteNonQuery()
        conn.Close()


    End Sub



End Class

Dies ist meine Datenbank-Tabelle 'users':

Bin ich immer diese Fehlermeldung:

Error   1   Operator '+' is not defined for types 'Double' and 'Date'.  C:\Users\Brian\Documents\Visual Studio 2012\WebSites\WebSite1\Registration.aspx.vb  51  19  WebSite1(1)

Kann mir jemand sagen, was Los ist ?