So your are trying to restore a database from the backup of another database with another name and you encounter this error.
Here is how you can overcome it.
Right-click on the database you want to restore.
“Restore Database” window opens.
For the 'Source' select 'Device' and browse to your .bak file.
For the 'Destination' select the database you want to restore.
Now on the left pane of this window click 'Options'
Choose “Overwrite the existing database” (WITH REPLACE)
Choose “Close existing connections to destination database”
Now you should be able to restore.
If you have further problems please check my post.
Hope this helps someone.