Did you try removing com.apple.iPhoto.savedState from HD/Users/you/Library/Saved Application State?

If that alone doesn't work then toss all of the prefs files etc along with that. If the thumbnails can't rebuild correctly you can try Quitting iPhoto then tossing anything in your iPhoto Library that has Thumb at the beginning, then launch iPhoto, it will rebuild them all.

Ctrl-click on the iPhoto Library then go to "Show package contents" to get to the innards.