The program Defiler (found here... SoulSeekkor's TQ Defiler - Home
) might fix your characters; its worth a shot anyway.
Basically run the program, then start Titan Quest. Get to the character select and be on your character but don't enter the game yet. Alt+Tab out to the Defiler program and select your character on its main menu. Click the fix character button then Alt+Tab back into game. Click the character switch button to select a different character and then switch back to the character you were trying to fix. Not sure why the procedure is set up as it is, but it has worked for characters who have used TQ Vault so far.
Basically the fix character thing is designed to make the game think your character is completely legit and has never been modified. Assuming you don't make changes to inventory such as TQ Vault, playing a custom map or editing your character with Defiler, theoretically you can play the character even with a new version of Titan Quest. Of course, doing any of the above can be fixed via the "fix character" option, so the game thinks they have not been done before.
Hope the program helps you. I found it in the modifications forum on the official game boards (http://www.titanquest.pro/forums/)
, which along with Banshee provide a ton of game information.