roundcube_bk problem

[stefano_ts]

Hello,
every 4 hours the file /var/lib/mysql/xxx.err reports this error:

Cannot open table roundcube_bk/cache
Cannot open table roundcube_bk/cache_index
Cannot open table roundcube_bk/cache_messages
Cannot open table roundcube_bk/cache_shared
Cannot open table roundcube_bk/cache_thread
Cannot open table roundcube_bk/contactgroupmembers
Cannot open table roundcube_bk/contactgroups
Cannot open table roundcube_bk/contacts
Cannot open table roundcube_bk/dictionary
Cannot open table roundcube_bk/identities
Cannot open table roundcube_bk/searches
Cannot open table roundcube_bk/session
Cannot open table roundcube_bk/system
Cannot open table roundcube_bk/users
... from the internal data dictionary of InnoDB though the .frm file for the table exists.

What is the folder roundcube_bk?
Can I delete or re-create it?
How can I fix this?
thank you.

Ps I opened this topic a week ago on the forum of cpanel but I have not yet received an answer...

[SKaero]

https://dev.mysql.com/doc/refman/5.0/en/innodb-troubleshooting-datadict.html