When attempting to archive forms using the Move Data job in Workflow Central Administration you encounter an error on the job stating "The root element is missing".
When auto archiving is turned on a column called WorkflowArchivedHistoryXML is created on all form items. Normally, the auto archiving mechanism will auto-populate this column with information once the process is completed. If the Move Data job is ran too soon, and this column is blank, the job will fail with the root element missing error.
Wait for the column to populate with information. This is performed by the createmhtjob which can be viewed in Manage Background Jobs on the Workflow Central Administration site. If the job is an error state, it cannot proceed and must be reset to pending.