When i try to execute queryProcessAnalytics inside Escalation timer rule event it change it's status to Paused by exception

I have a problem defination as "Escalation timer will start only when task is accepted by a user"
For that, I have created an expression rule which called queryProcessAnalytics to find if task is accepted by particular user or not and called that rule from escalation --> setup --> timer condition --> expression.
When user input task is executed it generate an alert  Error in Escalation Timer (ERROR:EVAL:@reason=index) and process status is changed to "Paused By Exception"
How do i resolve this?

P.S :- I have not used any sail function inside expression rule