Reports scheduled via Reports and Jobs run and suddenly the reports start failing.

Example Error in log:

Exception: Document already exists
Error RPT-0021: Error occurred while saving the report Capacity_vs_Demand_by_Resource_recurrence.PDF. Please contact your system administrator.

Example error in the BG log:

ERROR 2018-01-30 13:20:14,541 [Thread-212004] niku.njs (clarity:admin:21099943__D909634C-4F02-40BE-A89B-F6ADB666FE59:none) Error during adding file to DMS. com.niku.union.exceptions.DMSException: Document already exists:Capacity_vs_Demand_by_Resource_recurrence_13359899.pdf 

Steps to Reproduce:

1. Navigate to Home>Reports and Jobs 
2. Select a report from the list. 
3. Select Scheduled and uncheck Immediately under When. 
4. Select today's date and time for the start date 
5. Scroll down and select Set Recurrence 
6. Set the report to run via crontab, customer used "*/15 * * * *" to run every 15 minutes. 
7. Submit the scheduled report. 

Expected Result:  
Scheduled reports run every 15 minutes until paused or canceled. 

Actual Result:  
Reports run as expected for a period of time, then fail.  Once the scheduled report fails, it continues to fail. 

Caused by DE39624 

This is resolved in 15.7.1+

Workaround 1:
Generate the report in the background which is accessible from Reports and Jobs > Reports

Run the job as Scheduled.
Uncheck the 'immediate' option.
Set the date prior to the current date.


Workaround 2:
Schedule reports in Home > Advanced Reporting