QuicK Help Please Rich Textbox Problem!!!

Why doesn`t this work. Im trying to use this when getting information from a serial port it works to get info send but when it tries for the incoming it gives me an error of:

Cross-thread operation not valid: Control 'rtfTerminal' accessed from a thread other than the thread it was created on.

rtfTerminal is a rich textbox

This is my code:

Code:

---

        Private Sub Log(ByVal msgtype As LogMsgType, ByVal msg As String)
            rtfTerminal.SelectedText = String.Empty
            rtfTerminal.SelectionFont = New Font(rtfTerminal.SelectionFont, FontStyle.Bold)
            rtfTerminal.SelectionColor = LogMsgTypeColor(CInt(msgtype))
            rtfTerminal.AppendText(msg)
            rtfTerminal.ScrollToCaret()
        End Sub

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You can not access a control from a thread other than the one on which it was created. Take a look at this thread by jmcilhinney the subject.