Try creating a service and impose a blackout against it instead.
1. Go to Services | Service Builder | Add A New Category
2. Enter name (e.g. .NET site blackout) | Next | Finish
3. Expand the newly created service | Click the Add icon | Add component to this service | Add specific component | Drop down From and choose the type (e.g. .NET) | Search | On the filter field, type in the name of the site you want to include in the blackout service and check all the type you want to black out | Add components. Repeat for the other objects you are interested with.
4. Now go back to Setup & Support | Blackouts | Create a One-Time Blackout | Suspend Alarms | Services | Check the new service that you created | Complete the Wizard.