Implement Aggregation inside QueryProcess Analytics, while querying task report

I have a requirement to send consolidated escalation emails. One user can have multiple tasks assigned to him. But requirement is we cannot send individual escalation emails to users as its increasing their mail box volume. So Instead of default task escalation email,  I need to create a consolidated email which will show all the tasks assigned to a particular user in a single mail if task isn't completed within 2 days.

I have created a  task report &  I tried using grouping by task owner field  inside queryProcess analytics, but it isn't working , attached code image.
I am getting the below error message 
errorMessage"The aggregation query parameter is not supported. (APNX-1-4203-027)"

Please Help Me its Urgent.. TIA

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