Looping Through Items In A Folder

I am using this code:

VB:
Sub a()
Dim WB1 As Workbook, WB2 As Workbook, MyFile As String, Sep As String, WS As Worksheet
Dim R As Range, X As Integer, a As Range, b As Integer, rownum As Integer, WS1 As Worksheet
Dim R2 As Range, a2 As Range, row As Integer, sep2 As String, MyFile2 As String

[Code] ....

If I run this code without the miles of code i have between them, it loops through each workbook in the folder just fine.

However, I am getting a Runtime 5 error when it reaches Myfile = Dir() each time with my full code.

Here is the full code:

VB:
Private Sub CommandButton1_Click()
Dim WB1 As Workbook, WB2 As Workbook, MyFile As String, Sep As String, WS As Worksheet
Dim R As Range, X As Integer, a As Range, b As Integer, rownum As Integer, WS1 As Worksheet
Dim R2 As Range, a2 As Range, row As Integer, sep2 As String, MyFile2 As String
Sep = Application.PathSeparator

[Code] .....

Once again, I am getting the error message 3 lines from the very bottom ("MyFile = DIR()")