[Error]Too many open files

Hi, Everyone.
My name is Hoang, I had setup a server database use MySQL version 5.1.37-ndb-7.0.8a-cluster-gpl on Linux(CentOS 5.5).
I config MySQL :
[mysqld]
open_file_limit = 2048
table_cache =64
...

on System, i use command : ulimit -n --> 1024

the recent, i see "error 24: Too many open files" in log of mysql and i check number of files open of process mysql used to command
> cd /proc/<id_process_mysql>/fd
> ll | wc -l
>lsoft | wc -l --> result = 2048

I have increased the value of open_files_limit=6000, but then this error still repeat. i don't know fix this error, i hope you can help me!