سلام دوست عزیز.منم مشکل شما رو داشتم با استفاده از کد خودت ایرادهایی رو که داشت گرفتم و در اخر هم برام جواب داد.اینم کدش. موفق باشی
backup
 string command = @"BACKUP DATABASE [" + Application.StartupPath + "\\ensani.mdf] TO DISK = N'" + strFileName + "' WITH NOFORMAT, NOINIT,  NAME = N'accounting-Full Database Backup', SKIP, NOREWIND, NOUNLOAD,  STATS = 10";

                this.Cursor = Cursors.WaitCursor;

                SqlCommand oCommand = null;

                SqlConnection oConnection = null;



                string scnn = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirector  y|\ensani.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";

                oConnection = new SqlConnection(scnn);

                if (oConnection.State != ConnectionState.Open)

                    oConnection.Open();

                oCommand = new SqlCommand(command, oConnection);

                oCommand.ExecuteNonQuery();

                this.Cursor = Cursors.Default;

                oConnection.Close();




Restore
 SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirector  y|\ensani.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

                con.Open();

                string s1 = "ALTER DATABASE [" + Application.StartupPath + "\\ensani.mdf] SET OFFLINE WITH ROLLBACK IMMEDIATE";

                string s2 = "ALTER DATABASE [" + Application.StartupPath + "\\ensani.mdf] SET MULTI_USER";

                string query = "RESTORE DATABASE [" + Application.StartupPath + "\\ensani.mdf] FROM DISK ='" + strFileName + "' WITH RECOVERY,REPLACE";

                SqlCommand cmd = new SqlCommand();

                cmd.CommandText = s1;

                cmd.Connection = con;

                cmd.ExecuteNonQuery();



                cmd.CommandText = s2;

                cmd.Connection = con;

                cmd.ExecuteNonQuery();



                cmd.CommandText = query;

                cmd.Connection = con;

                cmd.ExecuteNonQuery();



                con.Close();