I have the expansion pack Kingdom of the Sky and I wanted to zone to it, but I get every time this error and if I want to return in game I have to delete my character because the client want to load that zone.
This is the zone that I wanted to check out...exp02_rgn_realm_of_dawn - The Barren Sky (Realm of Dawn)
And here is a screenshot from the error.

Yeah unfortunately were still having problems with some zones... If you get stuck you can do a query in the world database like:
update characters set current_zone='zonenamehere' where name='yourcharname';
we will have tools to make this easier soon.