Help in rewriting function to open linked workbook

Hi all:

An expert provided the attached function a few months ago.  It works great on my machine for my development purposes but isn't doing what I need it to do when I move things to the server.

Setup: In a directory on the server I have a few quoting workbooks that link to the materials.xls workbook.  All workbooks are set read only in the OS properties to prevent accidental saving of entered data.

Desired:  User1 opens up quote1.xls, which then automatically opens materials.xls.  The user may need to edit values in materials only for these quotes [changes will not be saved].  User1 opens quote2.xls which sees that materials.xls is already open & skips the attempt to open materials.xls.  User2 opens quote2.xls, which then opens materials.xls.  Here I do not need to suppress the dialogs from the OS stating User1 is using the files & do they want to open a read only copy.  The OS would then open an original copy of materials.xls for User2.

Problems:
a]  If materials.xls is set to read only by the OS properties, the current function does not open materials.xls
b]  If I don't use the existing function but instead open materials.xls with

Workbooks.Open Filename:=fileToOpen

the user is presented with a dialog to either re-open materials.xls [which will lose the temporary changes that may have been made] or sends them into VBA debug mode because the file is already open.
c]  Using the existing function; if User2 opens a quote workbook while User1 also has a quote workbook open, the function recognizes materials.xls is in use and therefore materials.xls is not opened.

Thanks in advance for your help.

Bob

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Private Sub Workbook_Open()
  Application.WindowState = xlMaximized
  Dim wb As Workbook
  Set wb = ThisWorkbook  
  Dim openPath As String
  Dim fileToOpen As String  
  openPath = ThisWorkbook.Path
  fileToOpen = openPath & "\Materials.xls"  
  If IsFileOpen(fileToOpen) Then
    'do nothing
  Else
    Workbooks.Open Filename:=fileToOpen
  End If
  wb.Worksheets("Start").Activate
End Sub
 
Function IsFileOpen(strFullPathFileName As String) As Boolean
  Dim hdlFile As Long
  '// Error is generated if you try
  '// opening a File for ReadWrite lock >> MUST BE OPEN!
  On Error GoTo FileIsOpen:
    hdlFile = FreeFile
    Open strFullPathFileName For Random Access Read Write Lock Read Write As hdlFile
    IsFileOpen = False
    Close hdlFile
    Exit Function
FileIsOpen:
    '// Someone has it open!
    IsFileOpen = True
    Close hdlFile
End Function