Restore SQL Server database
From the more complete error message:


  Cannot open backup device 'D:\AlomohasebSQL.bak'. Operating system error 2 (‏‏Invalid path). Msg 3013, Level 16, State 1, Line 1 RESTORE DATABASE is terminating abnormally. 


Do you know the exact SQL restore statement you are performing? No matter what front-end language you are using, it should be executing something like this against the SQL Server:

RESTORE DATABASE myDatabaseName
FROM FILE = 'D:\myDatabaseBackup.BAK'
WITH (various options here)


In your case, I think the error message indicates that the backup file location ("D:\AlomohasebSQL.bak" in your error above) is incorrect. Obviously, make sure this is a valid drive, path and filename. 

IMPORTANT NOTE: This path needs to be visible to the SQL Server, not to wherever you are running this app. (Thanks @ColinMackay for bringing this up). In a related note, check to see that the SQL Server service account has the proper permissions to read this file at that location.

There is a (smaller) possibility that it doesn't know where to place the database files after it restores them. SQL does have a "default" path, but this is sometimes out of date. If necessary you can specify the path to restore the files to:

RESTORE DATABASE myDatabaseName
FROM FILE = 'D:\myDatabaseBackup.BAK'
WITH MOVE 'primarydatafilename' To 'D:\DB\data.mdf', 
     MOVE 'logfilename' To 'D:\DB\log.ldf'


You'd obviously need to know the files that are part of that database. If you don't, just use the SSMS restore wizard. There are ways to find that via the RESTORE command, let me know if you need that.