What is the language of the PSTs that you are migrating? If PST Migrator needs to create folder names in the mailbox, it is important that it uses the same Windows codepage that was used when the PSTs were created.
If the language used was not Western European, and if the wrong codepage is used, limitations in Exchange Server mean that the folder names may be corrupted, although there is no problem with items within the folders.
To avoid these problems, select the language that was used when the PSTs were created. If the language is not listed, select and enter the codepage number.
Note that the selection you make here must be available on the Storage Service computer that is archiving the contents of the PST files. If you need to install extra languages, see the Microsoft Knowledge Base article HOW TO: Add and Enable Additional Languages in Windows.