Determine Last User Of Workbook

Trying to determine who has a file open, the code below works for simple files. However if the workbook contains macros and user forms it seems there are multiple occurances of the search terms strFlag1, strFlag2. How can I determine the last user

Function LastUser(path As String)
Dim text As String
Dim strFlag1 As String, strflag2 As String
Dim i As Integer, j As Integer
strFlag1 = Chr(0) & Chr(0)
strflag2 = Chr(32) & Chr(32)
Open path For Binary As #1
text = Space(LOF(1))
Get 1, , text
Close #1
j = InStr(1, text, strflag2)
i = InStrRev(text, strFlag1, j) + Len(strFlag1)
LastUser = Mid(text, i, j - i)
End Function

Above code taken from Determine Last User