My server locked up twice today (stopped pinging out of the blue). First reboot went into fsck mode successfully completed anyway.

/var/log/messages shows this:

Oct 7 03:30:03 server kernel: Fatal resource shortage: numiptent, UB 108.
Oct 7 05:40:03 server last message repeated 2 times
Oct 7 05:40:03 server kernel: Fatal resource shortage: numiptent, UB 108.
Oct 7 12:02:01 server kernel: VPS: 107: stopped
Oct 7 12:06:23 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Down
Oct 7 12:06:26 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Up 10 Mbps Full Duplex
Oct 7 12:06:38 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Down
Oct 7 12:06:40 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Up 10 Mbps Full Duplex
Oct 7 12:06:44 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Down
Oct 7 12:38:51 server shutdown: shutting down for system halt
Oct 7 12:06:23 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Down
Oct 7 12:06:26 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Up 10 Mbps Full Duplex
Oct 7 12:06:38 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Down
Oct 7 12:06:40 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Up 10 Mbps Full Duplex
Oct 7 12:06:44 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Down
Oct 7 12:38:51 server shutdown: shutting down for system halt
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised auto-negotiation: Yes
Speed: 10Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: umbg
Wake-on: d
Current message level: 0x00000007 (7)
Link detected: yes
It appears the main problem is:

Oct 7 18:46:56 server kernel: e1000: eth0: e1000_watchdog_task: NIC Link is Up 10 Mbps Full Duplex

Kernel: 2.6.9-023stab044.11-enterprise #1 SMP
O/S: CentOS release 4.3 (Final)

Hardware confirmed ok.