Вот текст скрипта, работает как надо
 
 
'=========================
'polyline_Set_M.cal
'Author: Ianko Tchoukanski
'
http://www.ian-ko.com'=========================
Dim pPoint As IPoint
Dim pPredPoint As IPoint
Dim pPolyline As IPolyline
Dim pPointColl As IPointCollection
Dim pNewPointColl As IPointCollection
Dim pMA As IMAware
Dim dM As Double
Dim i As Long
'==========================
'adjust the parameters below
dM = 0
'if M value from a field is to be used unremark the following line
'remove the quotation marks and adjust the field name
'dM = "[M_FIELD]"
'==========================
If (Not IsNull([Shape])) Then
  Set pPolyline = [Shape]
  If (Not pPolyline.IsEmpty) Then
    Set pPointColl = pPolyline
    Set pNewPointColl = New Polyline
    For i = 0 To pPointColl.PointCount - 1
      Set pPoint = pPointColl.Point(i)
 If i=0 Then
  pPoint.M=dM
 Else 
  Set pPredPoint= pPointColl.Point(i-1)
  dM = dM + Sqr((pPoint.X-pPredPoint.X)^2+(pPoint.Y-pPredPoint.Y)^2)
        pPoint.M = dM
 End If
        pNewPointColl.AddPoint pPoint
    Next i
    Set pPolyline = pNewPointColl
    Set pMA = pPolyline
    pMA.MAware = True
    End If
End If
 
_esri_field_calculator_splitter__
pPolyline