I had the same problem on Jaunty RC; "sudo update-apt-xapian-index" didn't work (I closed Synaptic), so I deleted /var/lib/apt-xapian-index/ and then the fix worked.
I had the same problem on Jaunty RC; "sudo update- apt-xapian- index" didn't work (I closed Synaptic), so I deleted /var/lib/ apt-xapian- index/ and then the fix worked.