In the leaked server data, Eavan will respond to the "@transServer" chat option. Apparently she would check you out and tell you if you're safe to transfer or not before you go off and try it.
When you choose that chat option, she runs the OnSelectTransServer() function (and for once we actually have the definition for it). This function checks your character (presumably your bank tab as well) for a few things.
1 - If you're engaged.
2 - If you're married.
3 - If you have items that are marked as /notTransServer/. (These are mainly bags.)
4 - If you have any unclaimed cash shop items (items in the menu not yet taken).
If any of these are true, you get told you cannot transfer.
If none of them are true, you get told you can transfer.
What's interesting is that G9S2 is when this feature was added (featureTransServer, according to the features file), which is a lot more recent than some of the really old dummied-out stuff in the game.
Unfortunately I can't find any evidence that this feature is enabled in NA... though that's partially due to mismatching feature strings so I can't find which feature it actually is.
EDIT: After wrestling with XML parsing for far too long, I've finally got a method to loop and sort crap by attributes automatically, so here's a list of all the items with the /notTransServer/ tag.