Similar bug: https://support.zabbix.com/browse/ZBX-1143
My forum reply: http://www.zabbix.org/forum/showthread.php?p=57202#post57202

zabbix_server logs that it needs a higher CacheSize and continues to poll webstats without any mention that the server is having a problem. My suggestion is to halt the server since it cannot collect stats or at the very least add "Error" to the problematic line for users to identify the problem:

-/opt/zabbix/sbin/zabbix_server [3372]: Configuration buffer is too small. Please increase CacheSize parameter.
+/opt/zabbix/sbin/zabbix_server [3372]: ERROR: Configuration buffer is too small. Please increase CacheSize parameter.

-21825:20091217:172845.548 Can't allocate shared memory for configuration cache.
+21825:20091217:172845.548 ERROR: Can't allocate shared memory for configuration cache.