Got the same problem (bug 605583) with a fresh install of Ubuntu 10.04 while trying to install Eclipse IDE.
I then managed to update my system without a problem (with apt-get update && apt-get upgrade), and also installed Eclipse IDE without a problem on this updated system.
Seems like this is only happening on a fresh system, or on the first use of the update system.
Got the same problem (bug 605583) with a fresh install of Ubuntu 10.04 while trying to install Eclipse IDE.
I then managed to update my system without a problem (with apt-get update && apt-get upgrade), and also installed Eclipse IDE without a problem on this updated system.
Seems like this is only happening on a fresh system, or on the first use of the update system.