When I try to create a category, the category is created but I get this message:

Warning: Cannot modify header information - headers already sent by (output started at /home/alkha4/public_html/blog/b2evocore/_class_dataobjectcache.php:439) in /home/alkha4/public_html/blog/admin/b2categories.php on line 247

b2evolution 0.9.2 - GPL License - ©2001-2002 by Michel V - ©2003-2004 by François PLANQUE

Can anyone help me in how to get rid of it?

Thanks