Task can fail for many reasons. Opening the "Task result" popup can give more detailed description of the possible error occurred. If task continues to fail contact Miradore support.
If task is not run at all the error may be caused by the "Scheduled task engine". "Scheduled task engine" writes an hourly log file for last seven days. Log files can be found from the Miradore server's folder %INSTALLDIR%\Logs. Contact Miradore support and provide these log files.