"Error" in main page

Dear all,

I installed gallery 2.3 a few months ago, and it worked perfectly. Today I access the gallery, and all I get is the very 'explicative' message "Error" in the main page. I tried to upgrade to 2.3.1, but nothing changed. I had a brief look at the source code of main.php, but couldn't find any "Error" string (probably its in some language file). I checked the file permission, and nothing has changed since I first installed it.

The website is
http://www.internationalhall.com/gallery2/main.php
so you can directly have a look.

Thank you very much for your attention and - hopefully - help!