What is the exact error?
it could be something wrong with the items, or something wrong with the PST file itself
you could try moving the items back, and re-trying and maybe dtrace MigratorServer to see if any errors are reported and what those errors are... possibly to do with message class or something making them ineligible to be imported

also common steps may be to run the SCANPST against them. If SCANPST does not find anything or correct anything, collecting the logging as suggested above will help you to identify the items it is tripping up on so you can manually open it up and clean it. In my expirence, SCANPST fixes the vast majroity of initial errors seen in PST migraitons when there is an issue with the PST itself. 

Let us know how it goes, if there are further questions, or if you worked it out. 

Thanks

Had same issue.

Verify you have enough storage on the EV-server. With me, storage location was full, and therefor closed.

There was no roll-over defined.

To fix, I move all messages from the folder mentioned back into the inbox, restart pst migration.