"Invalid Call or Argument" in While Loop using MyFile = Dir

Hi guys,
When running the following code, once all the files have been looped through, I occasionally get an "Invalid call or argument" error at the bottom "myFile = Dir" line. It happens only sometimes, and other times the code executes fine.
What could I be missing? I know without much more information its a bit vague, but where would you suggest I investigate as to the cause? I'm just about to stick On Error Resume Next above it, since it only ever occurs after all the workbooks have been looped through and the loop is completed anyway - But thats lazy... any idea?

''' Get the array of files (excel file types only using .xl* )
        Dim MyFile As String
        MyFile = Dir(MyFolder & "\*.xl*")
        
        ''' Start the file counter
        Dim fileCount As Integer
        fileCount = 0

 ''' Start cycling through the files
Do While MyFile <> ""
        ''' Do some stuff

        ''' On to the next workbook file
                MyFile = Dir
                fileCount = fileCount + 1
Loop

The only times I use "Dir" are already shown in the original post. But below is the full code inside the loop....

 Do While MyFile <> ""
                Debug.Print MyFile
                Debug.Print (InStr(MyFile, "backup"))
                
                '' If the filename doesnt include the word "Backup"
                If ((InStr(MyFile, "backup") = 0) And (InStr(MyFile, "Backup") = 0)) Then
                               
                
                ''' 1. Add the new formulas and template into the DB
                    Worksheets("ConformanceDBTemplate").Activate
                    ActiveSheet.Range(conformanceDBTemplateRange).Select
                    Selection.Copy
                    
                    Worksheets("CONFORMANCE DB").Select
                    Range("A" & newRecordRow).Select
                    ActiveSheet.Paste
                    
                ''' 2. Open each workbook
                    'Set wb = Workbooks.Open(Filename:=MyFolder & "\" & MyFile)
                    Set wb = Workbooks.Open(MyFolder & "\" & MyFile, True, True)
                
                ''' 3. Copy the reconciliation data from the Block Reconciliatoin file we are currently looking at
                    '''' First - Test to see if the Block Workbook has an X4 Reconciliation worksheet, if not, add it. '''
                    doesR2SheetExist = False
                    For Each ws In wb.Worksheets
                        If ws.Name = "X4 Reconciliation" Then
                          doesR2SheetExist = True
                        End If
                    Next ws
                    
                    wb.Activate
                    If doesR2SheetExist = True Then
                        wb.Worksheets("X4 Reconciliation").Select
                        Range(reconciliationDataRange).Select
                        Selection.Copy
                    Else
                        Call ADD_X4_SHEET
                        wb.Worksheets("X4 Reconciliation").Select
                        Range(reconciliationDataRange).Select
                        Selection.Copy
                    End If
                
                ''' 4. Paste the data over to the CONFORMANCE DB worksheet
                    Workbooks(confDBName).Activate
                    Worksheets("CONFORMANCE DB").Select
                    Range(x4ValuesBeginColumnLetter & newRecordRow).Select
                    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
                        :=False, Transpose:=False
                
                ''' 5. Input the date for the new record
                    Range("A" & newRecordRow).Value = newDate
                    Debug.Print newDate
                    
                ''' 6. Input the Fret Name, Ver Name & Bench for the new record
                    Range("D" & newRecordRow).Value = wb.Worksheets("Presentation").Range("C2").Value ' Fret Name
                    Range("E" & newRecordRow).Value = wb.Worksheets("Grade Blocks").Range("B2").Value ' Ver Name
                    Range("F" & newRecordRow).Value = wb.Worksheets("Grade Blocks").Range("B3").Value ' Bench                    
                    
                ''' 7. Close the workbook without saving
                    ' If we want to save, use this code: wb.Save
                    Application.CutCopyMode = False 'Clears the clipboard first
                    wb.Close (False)
                    
                    
                ''' 8. Update the newRecordRow
                    newRecordRow = newRecordRow + numberOfRowsPerRecord
                    
                Else
                    
                    backup_count = backup_count + 1
                
                End If
                    
                ''' 9. On to the next reconciliation workbook file
                MyFile = Dir 
                fileCount = fileCount + 1
        Loop