For our scheduled 24 hr time-span reports, we frequently get this message "Failed to retrieve distinct values for specific field across range x to xxx:500 Server Error."
I would suggest calling Tech Support for assistance with this issue. It does look like an issue I have come across before, where the fix was to adjust some settings in the nwconcentrator.conf file. Have a look at this SCOL note for the changes: https://knowledge.rsasecurity.com/scolcms/knowledge.aspx?solution=a64776
