This message means that your table needs repair, however, the option for repair through the phpmyadmin interface is not available.
Therefore, you need to open a terminal or ssh and run the following commands:
1) cd /var/lib/mysql/DATABASE (where DATABASE is the one containing the table that needs repair)
2) myisamchk –safe-recover TABLE (where TABLE is the table you are trying to repair)
Your table will be fixed in a few minutes!