Basic Worksheet object creation

[liquidroyl]

Hi all -

I am using Excel 2003 and have a very simple (in theory) macro that is supposed to display the name of the active sheet in a message box:

Public Sub DisplayActiveSheetName()
    Dim worksheet1 As Excel.Worksheet
    worksheet1 = ThisWorkbook.ActiveSheet
    MsgBox ("The name of the active sheet is: " & worksheet1.Name)
End Sub

This code resides in a Module.
When running this code, I receive the Run-time error '91' that the

    worksheet1 = ThisWorkbook.ActiveSheet

line "Object Variable or With block variable not set."

Any advice would be appreciated.

Thanks!