thanks for your anwers
i found out that the error was the memory allocated for a page, by default in php.ini is 8mb, i changed it to 16mb, as suggested in the FAQ.
my problem also was that i didnt know where to look for errors, my pages were blank, showing no error, and leaving me with little clue as to how to fix it.
i needed to look in my server error log, but where was it? in my linux (fedora core 2) it is in /var/log/httpd in a file called "error_log". i checked there and i was getting a memory allocation problem, the fix is also in the faq.
now i am facing a new problem.... but i will use a new thread for that
thanks
eliseo.