Error Select Method of Range Class Failed - vba

Question

My code aims to import an .xls file selected by the user, and copy and paste it into my Data sheet in Book 1. This Book 1 has 2 sheets: Results and Data.
I want to run the code when I am in Results and here comes the problem.
When I run it in my Data sheet, after clearing the current sheet (Data) the file is imported and copied well.
However, when I import it when I am in the Results sheet, it comes an error according to the MsgBox Err.Description
What's wrong in the code?
Sub ImportData()
Dim customerBook As Workbook
Dim filter As String
Dim caption As String
Dim customerFilename As String
Dim customerWorkbook As Workbook
Dim targetWorkbook As Workbook
Dim wb As Workbook
On Error Resume Next
Set wb = Application.Workbooks("Book1.xlsm")
wb.Activate
wb.Sheets("Data").Range("A1:M5000").Select
Selection.ClearContents
Sheets("Data").Select
Range("A1").Select
Set targetWorkbook = Application.ActiveWorkbook
filter = "Text files (*.xls),*.xls"
caption = "Please Select an Input File "
customerFilename = Application.GetOpenFilename(filter, , caption)
Set customerWorkbook = Application.Workbooks.Open(customerFilename)
Dim targetSheet As Worksheet
Set targetSheet = targetWorkbook.ActiveSheet
Dim sourceSheet As Worksheet
Set sourceSheet = customerWorkbook.ActiveSheet
sourceSheet.UsedRange.Copy targetSheet.Range("A1")
sourceSheet.UsedRange.Value = sourceSheet.UsedRange.Value
targetSheet.Paste
customerWorkbook.Saved = True
customerWorkbook.Close
Sheets("Results").Select
End Sub

Answer 1

You may try it like this...
Sub ImportData()
Dim filter As String
Dim caption As String
Dim customerFilename As Variant
Dim customerWorkbook As Workbook, targetWorkbook As Workbook
Dim targetSheet As Worksheet, sourceSheet As Worksheet
Set targetWorkbook = Application.Workbooks("Book1.xlsm")
Set targetSheet = targetWorkbook.Sheets("Data")
targetSheet.Range("A1:M5000").ClearContents
filter = "Text files (*.xls),*.xls"
caption = "Please Select an Input File "
customerFilename = Application.GetOpenFilename(filter, , caption)
If customerFilename = False Then
MsgBox "No Customer File was selected.", vbExclamation
Exit Sub
End If
Set customerWorkbook = Application.Workbooks.Open(customerFilename)
Set sourceSheet = customerWorkbook.ActiveSheet
sourceSheet.UsedRange.Copy
targetSheet.Range("A1").PasteSpecial xlPasteValues
Application.CutCopyMode = 0
sourceSheet.UsedRange.Value = sourceSheet.UsedRange.Value
customerWorkbook.Saved = True
customerWorkbook.Close
targetWorkbook.Sheets("Results").Select
End Sub

Answer 2

The following code:
wb.Sheets("Data").Range("A1:M5000").Select
Selection.ClearContents
Should be replaced with:
wb.Sheets("Data").Range("A1:M5000").ClearContents
The same goes for all similar lines. Operating on selection most often comes from macro recorder, is a very unreliable and slow method. It's dependent on currently selected range or object and non-transparent in the code, as it forces to know what is currently selected / active.
Selecting should be done only to leave selected worksheet or cell active in the end of macro operation or to perform actions on ActiveWindow.
Likewise, try to eliminate ActiveSheet:
Set targetSheet = targetWorkbook.ActiveSheet
And replace it with one of the following examples:
Set targetSheet = targetWorkbook.Worksheets(1) '1st worksheet in the file
Set targetSheet = targetWorkbook.Worksheets("myData") 'worksheet named "myData"