Did you install the modified hildon desktop at any point recently?

Is it related to this error? "E: Invalid record in the preferences file, no Package header"

To find out, open an xterm and do apt-get update. (You should always do this if you ever encounter problems with either the built in application manager or fapman)

If the answer is yes then either correct the /etc/apt/preferences file or just delete it.

If you get some other error then post it here : )