Server Application ‘/’ unavailable error
This is a generic error message. If this related to asp error (you can identify this by checking the error message under the Server application ‘/’ unavailable error)
1. Check the permissions for the domain folders. Assign Asp.net and network service permissions to it if it lacks.
2. If still the error persists, check whether the domain is assigned with an application pool. If it is not assigned, assign it.
3. Change application pool from shared to dedicated via CP.
4. Assign permissions to the application pool user for the domain.