I have a macro that manipulates the cells from 2
workbooks. It prompts for 2nd file to be open, do some
calculations, and then copy and paste some cells from 2nd
opened workbook to the 1st workbook. This procedure worked
fine when I run it from the .xls file. However, when I
have it as a add-in, this part did not work at all. I
tried debugging it, but it did not seem to recognize the 2
workbook files. My code is as follow:

Filename = Application.GetOpenFilename(FileFilter:=Filt,
Title:=Title)
'Exit if the dialog box canceled, else open file in new
workbook
If Filename = False Then
MsgBox "No file selected."
Exit Sub

Else
Workbooks.Open (Filename)
End If

Set wbOne = ThisWorkbook
Set wbTwo = Workbooks.Open(Filename:=Filename)

With wbOne
.Worksheets(1).Range("X9").Value = "Sample"
.Worksheets(1).Range("Y9").Value = "Name"
End With

'Copy range L10:L89 to X10

With wbTwo
.Worksheets(1).Range("O10").Copy
Destination:=wbOne.Worksheets(1).Range("AA10")
.Worksheets(1).Range("O20").Copy
Destination:=wbOne.Worksheets(1).Range("AA20")
End With

Thank you!