I have DTPO, and have the same problem: import (or archive) a large email collection goes for a few email folders then crashes. What do I do? This was one of the main functions for which I bought DTPO!
Is the mail you’re trying to import stored on a remote mail server? Ideally, the mail should be imported from a local source (ie. stored on your machine).
If your source is local, I would also open a Support ticket for this and send any crash reports and/or Console logs to help us troubleshoot the issue.