"Too many open files in system" problems

[Berry]

Hello guys!

I hope some of you, Linux guru's could help me with problem that I face from day to day.

I have had "Perfect Debian Sarge, with ISPConfig", upgraded to Etch, HE-VPS with 512MB RAM (guaranteed) etc. Now, every day around a 8PM there comes to server overload (CPU goes over 10-15) and server stops to respond for minute or two. Log files and my tries of shell commands return "Too many open files in system"

Please advise me how could I try to isolate the source of the problem? And maybe any idea what could be doing that problem?

Thank you in advance for any suggestion!