The Group Apply Results dialog is displayed after the Group Apply wizard has finished and the Display the results when I close the wizard option was checked:
The dialog displays a list of all of the mailboxes that were updated by the wizard and the status for each one. For each mailboxes, there is a node that can be expanded to display any errors that occurred, if there were any. Any of the nodes under the Errors node can be double-clicked to view the details of the related error. The results can also be saved to a log file by clicking the Save... button. Selecting the Only save details of the errors that occurred option will cause only mailbox or Public Folders that have errors to be included in the log file.