I had a problem with the pricing of an ITA LX itinerary recently as well (shows up on ITA, orbitz, and cheaptickets but isn't bookable on either of the latter two sites--prices higher). I e-mailed ITA about it and got a response saying there must be an error, but the error appears to continue surfacing.

To the OP:
If you click on questions/comments from the page showing the itinerary you are having trouble with, you can send a message to ITA staff--they'll get the info about what exactly you were looking at.