Issue: You are attempting to re-run a previously failed public folder migration request and receive the error “Only one PublicFolderMigration job is allowed at a time for an organization.”
You need to clear the previous migration request that failed by running the following command:
If you find there are failed requests, remove them:
Get-PublicFolderMigrationRequest | Remove-PublicFolderMigrationRequest -Confirm:$false
At this point you may decide you’d like to clear out any Exchange 2013 Public Folders content that may have been created on Exchange 2013 during the new-migrationrequest.
If you haven’t resolve the cause of the migration failure, then you may need to first troubleshoot the public folder migration.