Finding Missing numbers in a given range

So i have a problem with my codings and was wondering if anyone can help me.

Function FindingMissingNumber() As String

    Dim intX As Integer = Nothing
    Dim intY As Integer = Nothing
    Dim strSting As String = Nothing
    Dim strSqlQUery As String = Nothing
    Dim cmdSqlCommand As Data.SqlClient.SqlCommand = Nothing
    Dim rdrDataReader As Data.SqlClient.SqlDataReader = Nothing

    '------------------------------------------------------------------------------------------------------------------------
    '-> Process
    '------------------------------------------------------------------------------------------------------------------------
    strSqlQUery = "Select ExReportPolicyNo From DBReport Order by ExReportPolicyNo"
    Dim msSqlConnection As New Data.SqlClient.SqlConnection()
    'NOTE - You may need to CHECK your connection string!!! in the line below
    msSqlConnection.ConnectionString = "Data Source=SISBSQL\SISBSQL;Initial Catalog=ExceptionReport;User ID=sa;Password=123;"
    cmdSqlCommand = New Data.SqlClient.SqlCommand(strSqlQUery, msSqlConnection)
    If cmdSqlCommand.Connection.State = Data.ConnectionState.Closed Then cmdSqlCommand.Connection.Open()
    rdrDataReader = cmdSqlCommand.ExecuteReader()
    If rdrDataReader.HasRows Then
        Do While rdrDataReader.Read()
            intX = txtRangeLeft.Text
            intY = txtRangeRight.Text
            'intY = rdrDataReader.GetValue(rdrDataReader.GetOrdinal("ExReportPolicyNo"))

            Do While intX <> intY
                intX = intX + 1
                If intX <> intY Then
                    strSting = strSting & intX & ", "    'if it is not, then record the non sequential number into the string
                Else
                    Exit Do
                End If
            Loop
        Loop
    End If
    If cmdSqlCommand.Connection.State = Data.ConnectionState.Open Then cmdSqlCommand.Connection.Close()
    'return string
    Return strSting
    'tidy up
    intX = Nothing
    intY = Nothing
    strSting = Nothing
    strSqlQUery = Nothing
    cmdSqlCommand = Nothing
    rdrDataReader = Nothing

End Function

Basically i'm using VB.NET and MSSQL to make a program on finding missing numbers in between a given range set by the user. The program will read from the table and give the output on a textbox. And the above codes are so far what i can come up with. But the problem is, i get wrong output and not what i want. Here's an Image[^] of the output.

As you can see the program loops it multiple times, and give out the wrong output. The output should read only "286118, 286120, 286121". Question is where did i went wrong?

Tags: Visual Basic, SQL Server, SQL Server 2008