user error: Duplicate entry 'locale:en' for key 1
query: INSERT INTO cache (cid, data, created, expire, headers) VALUES ('locale:en', 'N;', 1116171811, 0, '') in /var/www/free.fr/f/9/mems.cast/includes/database.mysql.inc on line 66.
warning: Cannot modify header information - headers already sent by (output started at /var/www/free.fr/f/9/mems.cast/includes/common.inc:384) in /var/www/free.fr/f/9/mems.cast/includes/common.inc on line 192.

What is this problem?

It appeared when I try to put some translating messages for multilanguage purpose.

Thanks in advance for your repply.