Last two lines are not valid keys -- set invidually of course the timeouts are fine, not sure where this meta-key comes into play.

cat /etc/sysctl.conf
net.ipv4.conf.default.arp_ignore=1
net.ipv4.conf.all.arp_ignore=1
net.ipv4.ip_forward=1
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv4.icmp_ignore_bogus_error_responses=1
net.ipv4.tcp_fin_timeout=30
net.ipv4.tcp_keepalive_time=120
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_timestamps=0
net.ipv4.ip_conntrack_tcp_timeouts="300 43200 120 60 120 120 10 60 30 120"
net.ipv4.ip_conntrack_udp_timeouts="60 180"

$ sysctl -p
root@OpenWrt:~# sysctl -p
kernel.panic = 3
net.ipv4.conf.default.arp_ignore = 1
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.ip_forward = 1
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 120
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_timestamps = 0
sysctl: error: 'net.ipv4.ip_conntrack_tcp_timeouts' is an unknown key
sysctl: error: 'net.ipv4.ip_conntrack_udp_timeouts' is an unknown key