Job invoked by Alert but Alert never occured

I have a problem with an Alert that is supposed to invoke a Job. Here
are some details:

Windows Server 2000
SQL Server Standard Ed. ver. 8.00.818 (Sp3)
Alert: SQL Server performance condition alert; Counter: Percent Log
Used; If the counter rises above 90% the response is to execute Job.
Job: Transaction Log backup; set up through the Database Maintenance
Plans.  This job runs a backup hourly during the day, on a couple of
the Databases; yet also runs if the Alert is triggered. (This part
works fine.)

The problem I am encountering is where the job is running because it
was invoked by Alert 10. Yet, the Alert (10)registers Zero occurances.
The Job will then start getting into a cycle where the Job launches
every minute stating the whole time that Alert 10 invoked it.

How do I get this job to run only when scheduled and/or when triggered
by the alert?

Thank you,
Stephanie