Import asp.net / SQL Server 2012 website database to local SQL Server 2014 express
This could be caused by any number of issues.

To help get to the bottom of this I would, In SSMS open a new query window and run the following command

RESTORE DATABASE [DatabaseNameHere] 
FROM DISK='Path to the backup file here'


e.g. if my database was called AdventureWorks and the backup was located in c:\Temp\Adventureworks.bak the TSQL would be.

RESTORE DATABASE [AdventureWorks] 
FROM DISK='c:\Temp\Adventureworks.bak'


The error produced will give you a much better indication as to what the issue is.