Go and look at the Scheduled task page (the right hand column will have 84600 in the retry time column) and the Scheduled Task logs to see what is going wrong.
I thought Mary answered this question. You can't do what you want to do. You're looking (I think) for a feature called "multi tenancy" which standard Moodle doesn't have.
You would need Moodle Workplace or www.iomad.org for that.