In reply to Annie Conbou.

If you have any plugins installed which use "shortcodes", try deleting them and see if that automatically fixes it.

I put shortcodes in quote marks above, as the plugin probably isn't using actual WordPress shortcodes, but is using it's own system instead.

If you can pinpoint a problem plugin, then go see if there is an update for it. If there is no update available, or if an update doesn't fix the problem, then post a question in the WordPress.org support forums about it and post a link to it here. If no one on dot org beats me to it, then I'll take a look at the code and try to work out a fix for you.