Database Software

I am trying to call wb_rt_api_exec.run_task as the repos owner, i do excatly as the documentation says and it fails with the above error. When i call the script oem_exec_template, which only calls this procedure it succeeds!

I have tried working through the script in sqlplus, eg setting roles and session and still fails if i call the proc in SQLPlus. why is this? and can i get around it as Id obviously prefer to call the stored proc rather than a text file script.