Ever since a bit before today's maintenance and after it I've been having the same problem over and over, and not just me, but a whole lot of other people too looking at the contact list & the complains in the game.
What happens: After moving somewhere or teleporting "Istaria.exe is not responding", the game just straigh-out freezes. Now if it only happens once, that'd be ignorable, but then you log back in and 2 seconds after the loadingscreen is gone, or even during sometimes, "Istaria.exe is not responding".

And then you try to login once more... Loading in, Loaded succesfully, move one step forward: "Istaria.exe is not responding".

So then I'm forced to log in with another character to continue playing until a few minutes passed and I can succesfully log in without "Istaria.exe is not responding", only to have it happen later again on the same character and/or on another character. Not too long ago I almost ran out of characters to log in because they all had the same problem: "Istaria.exe is not responding".