Comment 1 for bug 705944

Seems like your search index got corrupted somehow, to fix it open a terminal and run these commands:

zeitgeist-daemon --quit
cd ~/.local/share/zeitgeist/
rm -rvf fts.index/
zeitgeist-daemon &

Afterwards your database will be reindexed, wait a while for this to happen (there'll be lots of output in the terminal) and then try again.