PokerTracker

'Cache update failure due to an invalid custom stat. You will be unable to import until the stat is fixed or removed.'

How do I find out which stat is invalid?

In the next release PT4 will list the invalid stats and columns. I don't yet have a release date for that, but in the meantime if you make a Backup of just the optional files (no databases) and attach it to a Support Ticket with a link to this thread we'll be able to take a look for you and should be able to let you know the problem stats.