If you have a server, with Windows 2003, one day you can find your server disconnected from network :).

It's exactly what I get. Simple reboot and server lost network connectivity.
Event log full with system errors like:

Event iD: 12291, SAM failed to start the TCP/IP or SPX/IPX listening thread

Event iD: 4292, The IPSec driver has entered Block mode. IPSec will
discard all inbound and outbound TCP/IP network traffic that is not permitted
by boot-time IPSec Policy exemptions. User Action: To restore full unsecured
TCP/IP connectivity, disable the IPSec services, and then restart the
computer. For detailed troubleshooting information, review the events in the
Security event log.

Event iD: 7023, The IPSEC Services service terminated with the following
error: The endpoint mapper database entry could not be created.

When you check MS Knowledgbase for those errors you will find the following articles, the very popular are those:

http://support.microsoft.com/kb/930220
http://support.microsoft.com/kb/912023
http://support.microsoft.com/default.aspx?scid=kb;en-us;870910

BTW, apparently it's not caused by SP1. So, if you implemented all WORKAROUNDs mentioned in those articles, and server still disconnected from the network, try VERY simple solution :), changed RPC to start with localsystem instead of network service. Of course, remember to reboot your server :).