error messages from check box code...

Hi,
I am trying to use a check box in an excel sheet. However, this line of code:

If CheckBox2.Checked = True Then

produces the following error: Runtime error 424 - object required.
Why does Excel not recognise the check box as an object?

If I change the code to:

If ActiveSheet.Checkbox2.Checked = True Then
    MsgBox "true"
End if

The following error is returned: "Runtime error 438 - Object doesn't support thid property or method"

- what's going on? The correct sheet is selected, and the "Microsoft DAO 3.6 object library" is selected under references...

Lotte