I'm a novice script writer.  I am working on a script to extract tracking information from the comment line ShipGear puts in the invoice and populate the tracking table.  I've done the first little bit to identify the ShipGear comment line and display a message box.  It is a pre-write script.  Syntax check passes.
Any help on why I'm getting this error would be appreciated.  The error pops up after saying Yes to "ship all lines" 

Error 88           Invalid/unknown property name
O/S Error         Wrong number of arguments or invalid property assignment: ‘oBusObj’ (err/ret=2/0)
Program          SY_MAINT.PVC
Statement        3039
Class               SO_InvoiceDetail_Bus
Method            CallScript

Here's my script:

'Initialize variables sInvNo = "" : sTrackingID = "" : sItemType = "" : sComment = "" : sLineKey = "" nUPS = 0 : nFedEx = 0 : sMsg = "" : nEndComment = 0 : nPackageNo = 0 : nCurrPosition = 0

retVal = oBusObj.GetValue("InvoiceNo$",sInvNo)

'Find comment lines
retVal = oBusObj.MoveFirst()

Do Until cBool(oBusObj.EOF)  'loop through all lines and look for tracking number on ItemType 4 only  
     retVal = oBusObj("ItemType$",sItemType)   
     IF sItemType = "4" THEN   
         retVal = oBusObj("Comment$",sComment)   
         retVal = oBusObj("LineKey$",sLineKey)   

        'Identify ShipGear comment line   
               IF InStr(sComment, "SG:") <> 0 Then    
                    IF InStr(sComment, "End Shipment") <> 0 Then     
                    sMsg = "Line Key " & sLineKey & " is a ShipGear Comment"     
                    msgRetVal = oSession.AsObject(oSession.UI).MessageBox("", sMsg)     
                    END IF       
              END IF     
      END IF  

      retVal = oBusObj.MoveNext()   
Loop