That's a serious claim. How about you show us the code in and around the routine and your comments on the difference in the data between machines.

Allow External Access (checkbox in company maintenance).

The UDF on the Header will write to the first line of the Sales Order Line UDF then stops:

retVal = 0 : ocsVal = ""
HeadTN = "" : LineTN = ""

retVal = oBusObj.GetValue("UDF_TRACK_NO$",HeadTN) 'Getting Tracking No from Header

set oLines = oBusObj.AsObject(oBusObj.Lines)

retVal = oLines.MoveFirst()

Do Until oLines.Eof ' loop through all lines searching to write tracking no
retVal = oLines.SetValue("UDF_LN_TRACK_NO$",HeadTN)
retVal = oLines.Write()
retVal = oLines.MoveNext()
Loop