Calling Thread cannot access this object (Dispatcher.CheckAccess) - wpf

Question

I'm trying to use serial communication in WPF with vb.net and the only successful thing that I can do is sending data. When it comes to receiving data I have received different errors, and this one is the hardest for me to get over with. I tried to apply the windows form code when we want to receive data by using the Control.InvokeRequired, but since this is WPF this was transferred to Dispatcher.CheckAccess(). Everytime I load the program the transmission is ok but reception gives me error of System.InvalidOperation:'The calling thread cannot acces this object because a different thread owns it.' I looked at other solutions but none have worked.
Are there other solutions/process for receiving data from the other side?
I tried various examples from both windows document and other sites, but none was successful in WPF application.
Imports System.IO.Ports
Imports System.Text
Imports System.Threading
Imports System.Windows
Class MainWindow
Private WithEvents serport As New SerialPort
Private Delegate Sub SetTextCallback(ByVal [text] As String)
Private Sub onLoad()
Dim ports As String() = SerialPort.GetPortNames()
Dim port As String
For Each port In ports
comPortCombo.Items.Add(port)
Next port
End Sub
Private Sub ConButton_Click(sender As Object, e As RoutedEventArgs) Handles conButton.Click
'serport = New SerialPort()
If (comPortCombo.Text = "") Then
MessageBox.Show("Please select COM port!")
Exit Sub
End If
serport.PortName = comPortCombo.Text
serport.BaudRate = baudCombo.Text
serport.Open()
transButton.IsEnabled = True
conButton.IsEnabled = False
disconButton.IsEnabled = True
End Sub
Private Sub DisconButton_Click(sender As Object, e As RoutedEventArgs) Handles disconButton.Click
serport.Close()
disconButton.IsEnabled = False
transButton.IsEnabled = False
conButton.IsEnabled = True
End Sub
Private Sub TransButton_Click(sender As Object, e As RoutedEventArgs) Handles transButton.Click
serport.Write(transTextBox.Text & vbCrLf)
transTextBox.Clear()
End Sub
Private Sub serport_datareceived(sender As Object, e As SerialDataReceivedEventArgs) Handles serport.DataReceived
'recTextBox.Text = receiveserialdata()
'with serForm's function???
ReceivedText(serport.ReadLine())
End Sub
Private Sub ReceivedText(ByVal [text] As String)
If recTextBox.Dispatcher.CheckAccess() Then
Dim x As New SetTextCallback(AddressOf ReceivedText)
Dispatcher.Invoke(x, New Object() {(text)})
Else
recTextBox.Text &= [text]
End If
End Sub
'Function receiveserialdata() As String
' ' receive strings from a serial port.
' Dim returnstr As String = ""
' Try
' Do
' Dim incoming As String = serport.ReadExisting()
' If incoming Is Nothing Then
' Exit Do
' Else
' returnstr &= incoming & vbCrLf
' End If
' Loop
' Catch ex As TimeoutException
' returnstr = "error: serial port read timed out."
' Finally
' If serport IsNot Nothing Then serport.Close()
' End Try
' Return returnstr
'End Function
End Class
System.InvalidOperationException: 'The calling thread cannot access this object because a different thread owns it.'