I've got a boatload of file names that I need to update, and I was trying to do so using the Dir function.

What's weird is that, for some reason, "Dir" is currently returning Error Code 5, "Invalid procedure call or argument."

My code follows; any ideas why it's causing me trouble?

Option Explicit
Dim strPath, strFile, strMon, strFY As String
Dim i As Integer

Sub Populate()
    strFY = "FY" & Right(InputBox("What fiscal year?", "FY"), 2)
    For i = 1 To 12
        Select Case i
            Case 1
                strMon = "01Jul"
            Case 2
                strMon = "02Aug"
            Case 3
                strMon = "03Sep"
            Case 4
                strMon = "04Oct"
            Case 5
                strMon = "05Nov"
            Case 6
                strMon = "06Dec"
            Case 7
                strMon = "07Jan"
            Case 8
                strMon = "08Feb"
            Case 9
                strMon = "09Mar"
            Case 10
                strMon = "10Apr"
            Case 11
                strMon = "11May"
            Case 12
                strMon = "12Jun"
        End Select
        strPath = ThisWorkbook.Path & "\" & strFY & "\" & strMon & "\"
        Dir strPath
        While Dir <> ""
            If Left(Dir, 5) <> strMon Then
                Open strPath & Dir For Random As FreeFile
                Workbooks(strPath & Dir).SaveAs Filename:=strMon & Right(Workbooks(Dir).Name, Len(Workbooks(Dir).Name) - 5)
            End If
        Wend
    Next
End Sub