Object reference not set to an instance of an object.|| XML poster

I am getting error - Object reference not set to an instance of an object. when executing XML poster

1 XML Poster

<perform_travel_time>
<parameters>
<task_id>78691</task_id>
</parameters>
</perform_travel_time>

2- I have created Custom Metadata- Road_distances

3- created perform definition - perform_travel_time 

4- checked select * from Road_distances→ table exist