binding VBScript.RegExp

Ok i know that in vb i can just at a reference but this isn't in vb6 it's in a different application that uses code similar to VBA. so i need to do some regular expression testing and i'm doing the following and if i use the following pattern

(?<!,)\d{12, 20}(?!,)

it throws an error, but if i use something like
\d{12, 20}
it works fine... so does VBScript.RegExp not support look-ahead, behind ect.

VB Code:

'========================================================================
   'Functionality to check if tracking, order, pick tkt numbers and division 
   'seem to be truely valid
   Dim regex As Object
   Set regex = CreateObject("VBScript.RegExp")
   regex.IgnoreCase = True
 
   'Test OrderNo
   If Not IsNumeric(KfxOrderNo) Then
      bOrderNoValid = 0
   Else
      'Test expression
      regex.Pattern = "(?<!,)\d{12, 20}(?!,)"
      Dim xOrderNo As String
      xOrderNo = "tt123456789012tt" 'KfxOrderNo
      If Not regex.Test(xOrderNo) Then
         msgbox "shouldn't be here"
         bOrderNoValid = 0
      End If
   End If