Doh, my computer just crashed when running yum upgrade. Yum comlained about dependency resolution errors and protected multilib versions. A
yum update --skip-broken
did not help. What did help however was to run the command
package-cleanup -C -q --dupes
to check for which software packages are now installed twice. Then to remove the older version of each package by specifying the full file name, e.g.
yum remove libudisks2-1.94.0-7.fc17.x86_64 nspr-4.9-2.fc17.x86_64 nspr-4.9-2.fc17.i686
till package-cleanup does not show any duplicates any more.