Assume that you migrate public folders from a Microsoft Exchange Server 2007 server to a Microsoft Exchange Server 2013 server. After the migration, you try to remove the last public folder database from the Exchange Server 2007 server. In this situation, the running of the Remove-PublicFolderDatabase command fails.
This issue occurs because the PublicFolderMigrationComplete flag is set to True after the migration on the Exchange Server 2007 server. That causes a certain variable not to be populated, and this variable is necessary for removing the database. Therefore, a NullReferenceException exception is thrown.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about how to migrate public folders to Exchange 2013 from earlier versions, go to the following Microsoft website: