stored procedure not executed from scheduler job

I have a scheduler job that executes a stored procedure every minute. It has been working but it doesn't work any more and I have trouble finding why. There were no changes to the database schema. I can run the job manually and I can see the results from the executed job. However, letting it run on schedule shows a '+000 00:00:00' RUN_DURATION and did not produce any results.

BEGIN

  DBMS_SCHEDULER.create_job (

    job_name        => 'GSM_STATS_JOB',

    job_type        => 'PLSQL_BLOCK',

    job_action      => 'BEGIN gsm_stats_proc; END;',

    start_date      => SYSTIMESTAMP,

    repeat_interval => 'freq=minutely;interval=1',