Getting Overlapping error in Job Card. How to solve it?

When I click the Start Job button in Job Card I am getting following error:

Row 1: From Time and To Time of PO-JOB00063 is overlapping with PO-JOB00051

How can we solve this?

And why am I getting this error?

Surprising thing is that the PO-JOB00051 is already completed.