getting error "Object Variable or With block variable not set"

Question

I have created an Add-In for Excel which determines the name of ActiveSheet and ActiveWorkbook. The code I used is below. When I run the Add-In it is showing the above mentioned error after the message box "variables set". But when I run it in macros it is working fine. I don't understand what is happening with the Add-In. Could anyone help me with this?

Sub sheetvalues()
    Dim bk As Workbook, sht1 As Worksheet, sht2 As Worksheet, sht3 As Worksheet
    Dim book As String, sht As String, i As Integer, j As Integer
    Dim att(1 To 4) As String, att_col(1 To 4) As Integer

    MsgBox ("variables set")

    book = ActiveWorkbook.Name
    sht = ActiveSheet.Name
    MsgBox ("names set")

    Set bk = Workbooks.Add
    With bk
        .Title = "MissingValues"
        .SaveAs Filename:="MissingValues.xls"
    End With

    Set sht1 = bk.Sheets.Add
    sht1.Name = "EndOne"
    Set sht2 = bk.Sheets.Add
    sht2.Name = "EndTwo"
    Set sht3 = bk.Sheets.Add
    sht3.Name = "EndThree"

    MsgBox (book & "  " & sht)
    MsgBox ("completed")
End Sub

Answer 1

A common issue that causes this issue is forgetting to use 'Set' with assigning a value to a variable.