PostgreSQL 8.4.9

I am seeing errors from time to time in PostgreSQL's logs about a table called events. The events table is used to stores information generated by triggers in Zabbix everytime a specific event occurs on a server that is being monitored.

Zabbix is the only application using the database server.

Here is the error

INSTRUCTION : insert into events (eventid,source,object,objectid,clock,ns,value,value_changed) values (6393428,2,3,38,1353354000,0,1,0)
ERROR: duplicate key violates unique constraint « events_pkey »

Question

What steps can I take to resolve this error?

On dba.stackexchange.com, I have been told to add a sequence to Events, what effect would that have?

Code:
ALTER TABLE events ALTER COLUMN eventid TYPE bigserial;

http://dba.stackexchange.com/posts/29043/edit