The above title isn’t a surprise for anybody working in IT, but unusually for Public Folders, this one has a fairly simple fix!

The situation is thus; when attempting to complete a Public Folder migration to Office 365, you come across the following error:

Before finalizing the migration, it is necessary to lock down public folders on the legacy Exchange server (downtime required). Make sure public folder access is locked on the legacy Exchange server and then try to complete the batch again.

The problem with this error is that you have already locked down Public Folders on the legacy Exchange Server by running:

Set-OrganizationConfig -PublicFoldersLockedForMigration:$true

So what’s an admin to do when they’ve already run the command they are being told needs to be run?! Some googling may lead you to the idea of rebooting the server, or restarting the Information Store. Both of these will work, but a much simpler solution is simply to dismount the Public Folder database/s, and then mount them. The PFs are already locked so are unavailable to the users so there is no negative impact of doing this.

TL;DR – turn it off, and turn it on again.