Comeback from mysql 4.1 to 4.0

I get these errors:
[/]# tail -f /var/log/mysqld.log
050402 3:47:13 /usr/sbin/mysqld: Can't open file: 'help_keyword.MYI'. (errno: 142)
050402 3:47:13 /usr/sbin/mysqld: Can't open file: 'help_topic.MYI'. (errno: 142)
050402 3:47:13 /usr/sbin/mysqld: Can't open file: 'tables_priv.MYI'. (errno: 138)
050402 3:47:13 /usr/sbin/mysqld: Can't open file: 'time_zone_name.MYI'. (errno: 142)
050402 4:15:29 /usr/sbin/mysqld: Can't open file: 'columns_priv.MYI'. (errno: 138)
050402 4:15:29 /usr/sbin/mysqld: Can't open file: 'help_category.MYI'. (errno: 142)
050402 4:15:29 /usr/sbin/mysqld: Can't open file: 'help_keyword.MYI'. (errno: 142)
050402 4:15:29 /usr/sbin/mysqld: Can't open file: 'help_topic.MYI'. (errno: 142)
050402 4:15:29 /usr/sbin/mysqld: Can't open file: 'tables_priv.MYI'. (errno: 138)
050402 4:15:29 /usr/sbin/mysqld: Can't open file: 'time_zone_name.MYI'. (errno: 142)

How to fix?

 

 

 

 

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