I purchased roundtrip tickets through orbitz a couple months ago to Las Vegas from Indiana through orbitz for a very low price so sometimes the fares are valid.
Have you tried going directly to the airline's website? I sometimes use sites like orbitz and travelocity to do a general fare search, but then book directly through the airline. Many of the fares shown by those booking sites can also be booked directly.
I have found the same problem, many of the fares posted on ORBIZ are not valid at there site, or the airlines site.
I have seen this happen many times, the same posted fare will stay up for days with no ability to purchase tickets.
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