yum and rpm stop doing their magic because of corrupt files etc and no updates can be performed on the system. A simple, but maybe not recommended solution is to delete the files located in /var/lib/rpm

-rw-r--r-- 1 root root        0 Jan 22 10:10 __db.000
-rw-r--r-- 1 root root    24576 Jan 19 17:12 __db.001
-rw-r--r-- 1 root root  1318912 Jan 19 17:12 __db.002
-rw-r--r-- 1 root root   450560 Jan 19 17:12 __db.003

This solution does most likely work in other rpm based distributions.