Unable to access to plugin admin page...

Greetings. I have just installed Omeka and although everything run fine, when I try to access at plugin administration (http://historiaabierta.org/sintrenal/admin/plugins) the browser show me a 500 error. There is some plugins that I really need to this project, so I can't leave the site just like that. I have another project (http://apc.historiaabierta.org/) and the plugins administration works fine... is something missing? could be a trouble with PHP fileinfo extension?