Well somehow the restored file is corrupted. Maybe because mysqld was still running while restoring the database on filesystem level.
Did you have a look at that mysql.com link? especially the part:
Quote:
Stop the mysqld server with mysqladmin shutdown, run myisamchk --silent --force */*.MYI from the data directory to check all MyISAM tables, and restart mysqld. This ensures that you are running from a clean state. See Chapter 5, Database Administration.
Mind you i am guessing here, i have no real experience with this error.
But maybe a new restore would be a more secure way to go, if ofcourse the backup itself is not corrupt.