Why My Change Password File Gives Error How I Can Some This Error

Imports System.Windows.Forms
Imports System.Data.SqlClient
Imports System.Data

Public Class frmlogin
    Dim con As New SqlConnection("Data Source=Tarun-PC;Initial Catalog=bdsdb;Integrated Security=True")
    Dim da As SqlDataAdapter
    Dim ds As DataSet
    Private Sub frmlogin_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        txtusername.Focus()
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles btnclear.Click
        txtusername.Clear()
        txtPassword.Clear()
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
        Try
            da = New SqlDataAdapter("select Username ,Password from tblloggin where Username='" & txtusername.Text & "' and Password='" & txtPassword.Text & "'", con)
            ds = New DataSet()
            ' if da return more then 0 row there is a user then he can login 
            ' otherwise he cant becoz no user exist in databases
            da.Fill(ds, "tblloggin")
            'da.Fill(ds)
            If (ds.Tables("tblloggin").Rows.Count > 0) Then
                frmmain.Show()
                Me.Close()
                frmwelcome.Close()
                ' Me.Hide()
            Else
                MessageBox.Show("Incorrect Username and Password", "tblloggin")
            End If

        Catch ex As Exception
            MessageBox.Show("Invalid Operation can not be process")
        End Try
    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        Me.Close()
    End Sub
End Class

Imports System.Data
Imports System.Data.SqlClient

Public Class frmchangeprofile
    Dim con As SqlConnection

    Dim cmd As New SqlCommand

    Dim username As String
    Dim password As String
    Private Sub frmchangeprofile_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        con = New SqlConnection("Data Source=Tarun-PC;Initial Catalog=bdsdb;Integrated Security=True")
        con.Open()
        username = frmlogin.txtusername.Text
        password = frmlogin.txtPassword.Text
        txtcpusername.Enabled = False
        txtcpusername.Text = username

    End Sub

    Private Sub btnChangeSubmit_Click(sender As Object, e As EventArgs) Handles btnChangeSubmit.Click
        Try
            If txtcpoldpassword.Text = "" And txtcpnewpassword.Text = "" And txtcpconfirmpassword.Text = "" Then
                MessageBox.Show("Any of the fields can not be left blank")
            ElseIf txtcpoldpassword.Text <> username Then
                MessageBox.Show("Invalid Old Passsword")

            ElseIf txtcpnewpassword.Text <> txtcpconfirmpassword.Text Then
                MessageBox.Show("New Password and Confirm Password does not match")
            Else
                cmd = New SqlCommand()
                cmd.CommandText = "update tbllogin set Password ='" & txtcpnewpassword.Text & "' where Username= '" & username & "'"
                cmd.Connection = con
                cmd.ExecuteNonQuery()
                MsgBox("Password Change successfully")
            End If
        Catch ex As Exception
            MessageBox.Show("Performed Action Cannot be processed")
        End Try

    End Sub

    Private Sub btnClear_Click(sender As Object, e As EventArgs) Handles btnClear.Click
        txtcpoldpassword.Clear()
        txtcpnewpassword.Clear()
        txtcpconfirmpassword.Clear()
    End Sub

    Private Sub btnClose_Click(sender As Object, e As EventArgs) Handles btnClose.Click
        Me.Close()
    End Sub
End Class