If I'm interpreting your problem  correctly...

To use the add-in, you need to activate it for a given workbook  using
>Tools>Addins. Then, things such as "Active Workbook" will have a
context. As a stand-alone, the add-in will not have those things,
because it is NOT a normal workbook. It is just a collection of
functions and subroutines that can be "added in" to any workbook.