It's my first message on the board but i'm quite sure not the last

From time i'm playng with zoneminder and last week I setup a very strong system with 9 2MPX H.264 cams (1600x1200) in mocord.
The server it's a Intel I5 Quad Core with 4GB of RAM, 2TB HDD, gigaeth, Ubuntu 12.04 lts ( before just shell and now with Lubuntu) and ZM 1.25
Cameras are connected with a hyperlan 300Mbps network...
I take for this work n.5 2MPX cameras 1600x1200 ( china but very very nice) and n.3 Vivotek 8161 2MPX 1600x1200, both configured with 5FPS and H.264 codec.
All seems to work perfectly with console load of almost 5%, but sometimes I can found events from encoding errors like this I have tried to update ffmpeg
to modify shmax to 1GB but nothing can help to to solve...
I exclude hyperlan network because 2 cameras are directly connected to the server but with same encoding problem.
Zoneminder's log it's clear from error...
Can someone help me to found the trouble?
Could be too less powerfull the CPU for 9 hi res mocord channel???