I've been having trouble importing hand histories from 24hPoker (Entraction Network) to PokerTracker3 recently and after a bit of experimenting and a bit of help from PokerTracker support I've finally got to the bottom of it. Just incase anyone else is having similar trouble here's what the problem was:
The username part of the log-in screen is not case sensitive so I've been logging in as baggers59 when my correct username is Baggers59 (note the capital B). The problem with that is, whatever you type in on the log-in screen gets used in the hand histories files and if it's not exactly right PokerTracker (and presumably Hold'em Manager) won't recognise your username.