Service Zabbix agent using too much CPU

[dkmark]

Dear All,

For windows server I want monitoring security event logs.
But after item was added zabbix agent started using too much CPU(about 80%).
In log I see a lot of string like this

  2688:20120120:192406.759 zbx_open_eventlog() pNumRecords:131124 pLatestRecord:798305381
  2688:20120120:192406.759 End of zbx_open_eventlog():SUCCEED
  2688:20120120:192406.759 In zbx_get_eventlog_message() which:798336244
  2688:20120120:192406.759 End of zbx_get_eventlog_message():SUCCEED
  2688:20120120:192406.759 End of process_eventlog():SUCCEED
  2688:20120120:192406.759 In process_eventlog() source:'Security' lastlogsize:798336244
  2688:20120120:192406.759 In zbx_open_eventlog()

I tried change item(add maxlines = 10), but it's didn't help.
Do you have any ideas, how I can fix this problem?

Thank in advance.