I have just tried to create an account on your Clipperz installation,
and I could get the following error log using Firebug:
> Call to undefined function: json_decode() in
> /home/httpd/vhosts/ids.com.br/httpsdocs/clipperz/php/index.php
> on line 225
It looks like your PHP installation is lacking the json_decode function.
Hope this helps.
Best regards,
Giulio Cesare