if action without any send messages (only execute script):
18577:20100309:191707.869 [Z3005] Query failed: [-1] ORA-01400: cannot insert NULL into ("ZABBIX_TEST"."ALERTS"."USERID")
[insert into alerts (alertid,actionid,eventid,clock,message,status,alerttype,esc_step) values (12269,93,8662288,1268144227,'domain: /usr/local/sbin/...."',1,1,0)]

alerts create with USERID NOT NULL;

if mediatype not defined for one of the users
18577:20100309:191708.102 [Z3005] Query failed: [-1] ORA-01400: cannot insert NULL into ("ZABBIX_TEST"."ALERTS"."MEDIATYPEID")
[insert into alerts (alertid,actionid,eventid,userid,retries,clock,subject,message,status,alerttype,error,esc_step) values (12271,38,8662324,11,3,1268144228,'Statistics ....: PROBLEM','Date: 2010.03.09-19:17:08
Age: 5m
Host: .....

alerts create with MEDIATYPEID NOT NULL;