submit data from php: error with special character in the posted text

I am using an open source sw for a test forum, but if I insert in my message some special character like à,è,ì ... when I submit the topic I get the following error message:
Error in posting
DEBUG MODE
UPDATE elca2Forum_posts_text SET post_text = 'la città', bbcode_uid = '04e1371840', post_subject = 'prova accentate' WHERE post_id = 14
Line : 282
File : functions_post.php

The message are inserted/updated in a posgresql db.
Any suggestion?
thanks luciano