ANSWER:

I also use k-notes and have had this happen once before. It happened again right before the weekend, and I have just fixed it again.

The file you want is in ~/Library/Preferences/ and is named widget-com.rakoth.lichlord.widget.k-notes.plist

I recommend going into Time Machine, selecting this file, and hitting command-option-i — in the inspector window, pay attention to the byte size of the file. Then go back in time until you see a big jump in the file byte size. That will be your uncorrupted plist. Restore it.

Then restart your computer. I tried several times to restore it and then only restart the dashboard, but then bringing up the dashboard again only caused more corruption and blank notes. Restarting the computer gave me no corruption when I brought up the dashboard.

by Peter Ahlstrom from http://superuser.com/questions/415746