Personally, I don't see Ticket To Europe conflicting with Ticket to Ride: Europe. If it was Ticket to Europe: Ride then fair enough, but otherwise we're saying that all words/phrases have a margin around them, which I disagree with.
That was also our way of thinking when we chose the title for our game. However, perhaps we do not know enough about the law and are now learning a lesson.
Have you received a cease and desist letter from Days of Wonder? If not, then it cannot be a legitimate trademark violation. In the US they must defend their own trademark with a lawsuit or threat of one. If you are in Europe then your country may be different.