There is a known issue with these functions on Access 2000:
   FormatCurrency(),
   FormatDateTime(),
   FormatNumber(),
   FormatPercent(),
   InStrRev(),
   MonthName(),
   Replace(),
   Round(),
   StrReverse(),
   WeekdayName()
Microsoft has an k.b. article covering this:
   http://support.microsoft.com/?id=225956

You would expect that a fully patched A2000 machine (both SR3 for Office
2000 and SP8 for JET 4) would not have the problem. I got caught also: my
dev machines do not have the problem, but a fully patched client does!

I was not able to identify the difference. (Perhaps it's because I have
later versions of Access on my machines as well?)

The workaround is to create a a wrapper function in VBA, and call that
instead:

Function ReplaceX(varIn As Variant, strFind As String, strReplace As String,
_
Optional lngStart As Long = 1, Optional lngCount As Long = -1) As Variant
   'Purpose:   Wrapper for Replace() which has problems in Access 2000.
   '           Also handles nulls (in and out.)

   If Len(varIn) > 0& Then
       ReplaceX = Replace(varIn, strFind, strReplace, lngStart, lngCount)
   Else
       ReplaceX = Null
   End If
End Function