1. Go to Maintenance | Security Settings | User Maintenance and locate the user.
2. Locate a column called rpt access. If the user have rpt access set to 99 then that's mean they have access to all reports. Enter 0 if you do not want the user to have access to any report at all.
3. Filter out the criteria so that the report will be smaller
We will address this issue to 5.8.1. Unfortunately we rely on third-party tool (Jasperreports) that has a problem with generating huge report. In 5.8.1 we will introduce global parameter - max number of rows for report. If report request exceeds max number of rows the there will be user-friendly error to put additional criteria to a filter to decrease the number of retrieved rows. That should prevent Central Agent from crashing.