SNMP MIBS no longer found after reboot

[chojin]

I have added a bunch of MIBs for a device (Brocade FC switch) into /home/zabbix/.snmp/mibs.
After a restart of the zabbix_server everything works perfectly and those mibs are used.
However after a server reboot, the zabbix_server.log file is flooded with messages like this:

Cannot find module (SW-MIB): At line 0 in (none)
snmp_build: unknown failure 15112:20120829:175230.930 SNMP item [swOperStatus] on host [xxx] failed: first network error, wait for 15 seconds
snmp_build: unknown failure 15102:20120829:175232.981 SNMP item [swOperStatus] on host [xxx] failed: first network error, wait for 15 seconds
No log handling enabled - turning on stderr logging
Cannot find module (SW-MIB): At line 0 in (none)

When I manualy log in as user zabbix, and I try snmptranslate :

snmptranslate -On -To SW-MIB::swOperStatus
.1.3.6.1.4.1.1588.2.1.1.1.1.7

It just works..

Why doesn't it work in zabbix (v2.0.2) anymore after reboot? how to debug this problem?