Office 2007 SP1; XP Pro SP2

I have the following code to determine if a given path has been mapped on a
user's machine:

Function fn_Test_4_Drive() As Integer
fn_Test_4_Drive = 0 'Drive does not exist
Dim fs, d, dc, n
Set fs = CreateObject("Scripting.FileSystemObject")

Set dc = fs.Drives
For Each d In dc
' Debug.Print d.sharename
If InStr(1, d.sharename, "\\crpatlfnp03\temp") 0 Then
fn_Test_4_Drive = 1
Exit Function
End If
Next d

ret = MsgBox("It appears you do not have a connection to the drive
\\crpatlfnp03\temp." & Chr(13) & _
"Please get this drive mapped for future wires.", vbOKOnly, "Missing
drive!")

End Function

Several users have the test to fail, even if the drive is mapped.

Initially I used an if fs.folderexists test, but it gave me the same
erroneous results so I went to the above Function.

Note the debug print that I used to confirm that the d.sharename being
returned was indeed the value being tested for.

Is there any reason these tests should function on some machines but not on
others?

All machines are running Office 2007 SP1; XP Pro SP2