[qtranslate] Error translating some posts

Hi

I am using qtranslate to display the website in several languages. Today I decided to update to the new WordPress version, and I realised the plugin displays an error line when it tries to print information from some posts. The error line is:
Catchable fatal error: Object of class WP_Post could not be converted to string in /usr/home/ipd2004.com/web/wp-content/plugins/qtranslate/qtranslate_core.php on line 455
The curious part is that, out of 5 languages I have, Czech is working perfectly, although it is not the default one, but not the others. I also have the widgets Recent posts and Tag Cloud, and they are also only displayed in Czech version. How could I solve this issue? Any idea?

Thank you