How many Models?

Is it possible to use the same Model in both the main webapp AND an damin module? If so, How?

Yes sure, they are automatically included (‘application.models.*’), so you can just use it!

I regenerated the model in ‘application.models’ through gii. then regenerated the crud into admin module.

When I go to: http://localhost/adxc-netbeans/admin/announcements

I get: Announcements and its behaviors do not have a method or closure named "tableName".

but public function tableName() is in the model.

I am not sure how you are trying to access the function, paste your code maybe?