[CentOS] use of conntrack-tools

hi

i would like to use conntrack_tools on my centos server.
i use the rpms from centalt
but when i launch

conntrack -C
I got
conntrack v0.9.13 (conntrack-tools): Can't open 
/proc/sys/net/netfilter/nf_conntrack_count

Does someone already succeed in using it?

Thanks in advance for any answer