Hey Simon,
Okay, new zip attached with all the following files:
-Control.xla
-Auth.mdb
-TestBook1.xls
-TestBook2.xls
Open TestBook1.xls with macros disabled. Update the path in the ThisWorkbook module to where you'll store the xla file. (Does not have to be in the standard locale, I don't believe. Haven't tested this completely through.) Save it and reopen it.
You should now get a message about not working from home, and the workbook should close. This is a good thing. Check your addins, and a new one should be installed. Go into the code of the Control.xla and update the database path.
I've converted the Control workbook to an xla, and added the class module to monitor events. I've converted the old Workbook_Open routine to a separate re-usable routine, and made the addin to ensure that it is installed.
Once it's running, open TestBook2.xls. If you're all authorized, you're good to go, else it should kick you out. There is no code in there, it's all controlled by the Control.xla class module code.
Thing is, you need to add the ThisWorkbook code to all 27 workbooks to ensure that they kick the home users.
It's not perfect, but it should do the trick to get you started.
One issue now remains... if the user disables macros the first time, they won't get the add-in installed. We need to give you a way to ensure macros are enabled, and there's tricks for that.
Review this first, though, and ask your questions.