Admob doesn't work in Windows, only for Android and iOS.
So, it probably isn't in the Windows libraries.
And, if you updated your core AppGameKit, there are updates that need to be done to your Android (and Windows) projects as well.
For Android, there are a lot of changes that need to be accounted for in v1088 (as opposed to v1076).
You would have been better off creating a new Android AppGameKit directory and creating new projects from the Android templates on the
AGK Wiki Templates page. Then following the instructions on that pages for all of the changes that need to be made on a project-by-project basis (because you change the name and the package identifier for every project).
EDIT: You probably should have created a separate Windows AppGameKit install for the updated version (I have 5 different AppGameKit installs running side by side). Because there are some key changes in libraries and files specific to the projects. The Windows v1088 templates are on the same wiki page.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master