Error creating window handle

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VB

the error is coming from highlight sub for richtextbox:

        Highlight(Color.FromArgb(57, 135, 214), 0, "MOTOR")
        Highlight(Color.FromArgb(57, 135, 214), 0, "SCALLING")
        Highlight(Color.FromArgb(57, 135, 214), 0, "VALVE")
        Highlight(Color.Green, 0, "inputVariable")
        Highlight(Color.DarkOrange, 0, "outputVariable")
        Highlight(Color.Red, 0, "<descriptionFFB execAfter=")
        Highlight(Color.DarkRed, 1, "<FBDExchangeFile>")
        Highlight(Color.DarkRed, 1, "</FBDExchangeFile>")
        Highlight(Color.DarkRed, 1, "</FFBBlock>")
        Highlight(Color.DarkRed, 1, "<FFBBlock>")
Public Function Highlight(ByVal highlightcolor As System.Drawing.Color, ByVal fontstyle As FontStyle, ByVal WordsToFind As String)
      Dim FoundAtPosition As Integer
      If WordsToFind IsNot Nothing Then
          FoundAtPosition = GenCodeText.Find(WordsToFind, RichTextBoxFinds.None)
          Do Until FoundAtPosition < 0
              ' Highlight text
              ' Search next occurrence
              GenCodeText.SelectionColor = highlightcolor
              GenCodeText.SelectionFont = New Font("tahoma", 8, fontstyle)
              FoundAtPosition = GenCodeText.Find(WordsToFind, FoundAtPosition + 1, RichTextBoxFinds.None)

          Loop
      End If

this sub is highlighting around 1000 words inside my text"GenCodeText"....sometimes it is working and sometimes it is not......if i minimize the my text.....this error completely unseen.
so is there any way to exclude this error or to stop highlighting if it will happen or is there another better way to highlight inside RichTextBox.