Error restoring database backup

Sounds like the backup was taken on a machine whose paths do not match yours. Try performing the backup using T-SQL instead of the UI. Also make sure that the paths you're specifying actually exist and that there isn't already a copy of these mdf/ldf files in there.

RESTORE DATABASE MYDB_ABC FROM DISK = 'C:\path\file.bak'
WITH MOVE 'mydb' TO 'c:\valid_data_path\MYDB_ABC.mdf',
MOVE 'mydb_log' TO 'c:\valid_log_path\MYDB_ABC.ldf';

When restoring, under Files, check 'Relocate all files to folder'