If MigrationWiz fails to locate a Public Folder path that you know exists, the problem may stem from a trailing space in the folder's file path. To discover if this is the case, run the following PowerShell command. From the Exchange Management Shell on the migration Source computer, run the following:
Get-PublicFolder -Recurse -ResultSize Unlimited | select Identity | Export-Csv -Encoding Unicode Z:\folders.csv
This will identify locations in the Public Folder file path where there may be names with trailing spaces, and will output the information to a CSV file.