Compare Data Between Two Spreadsheets

I have two spreadsheets, and wish to compare some of the objects. I have my vba code set up in Sheet1, and my functions in Module1 in one spreadsheet. I successfully open up the second one, then get this error message:

Microsoft Visual Basic for Applications
Run-time error '1004':
Application-defined or object-defined error.

If I comment out the SwitchExcel line, the script works.

Here is my code:

Dim theRow As Integer
Dim theCol As Integer
Dim strVal As String
Dim LastCellRow As Long
Dim LastCellColumn As Long
Dim YesNo As Boolean

[Code] ..........

Module1 code consists of:

Code:
Function LastCellColumnNumber() As Long
''''''''''''''''''''''''''''''''''''''
' Last cell in column
''''''''''''''''''''''''''''''''''''''
Dim RowNumber As Long
Set WS = Worksheets("Sheet1")
With WS
RowNumber = 2
If .Cells(RowNumber, .Columns.Count) vbNullString Then
Set LastCell = .Cells(RowNumber, .Columns.Count)

[Code] .......