First, look at the Robot Schedule job log for the job. If the cause isn't apparent, look at the Robot Replay job log.
From the Robot Replay Main Menu, enter option 1.
From the Work with Replay History panel, enter option L to view the job log or enter option 1 to drill down to the virtual session job log.
Enter option L to view the job log or enter option 1 to drill down to the child job log.
If the cause still isn't apparent, look at the Replay object by taking option 5 to preview. This shows exactly what was learned into the Replay object. Then, in another session, look at the Replay object by entering option 11 to View History. Then find the instance of the object that failed, and enter option V to view the Visual Log. This shows exactly what screens came up when the Replay object ran.
Compare the screens learned in to the screens that came up in the Visual Log. If the images were changed or removed, the object must be relearned.