OverFlowException was unhandled by user code

Jeg bruger denne function som er fundet på nettet.
Men får fejlen:
*OverFlowException was unhandled by user code*
Tips:
Make sure you are not dividing by zero.

    Function CountWord(ByVal inputString)
        Dim pos, spaceCount
        pos = 1
        spaceCount = 1
        While Not pos = Len(inputString)
            If Mid(inputString, pos, 1) = " " Then    <--------- LINIEN HER ---------
                If Not pos = 1 Then
                    If Not Mid(inputString, pos - 1, 1) = " " Then
                        spaceCount = spaceCount + 1
                    End If
                End If
            End If
            pos = pos + 1
        End While
        CountWord = spaceCount
    End Function


Håber nogen kan hjælpe mig videre.....