iPhoto claims there is an update available iPhoto came with my Mac. It is currently version 9.1.1.

When I open iPhoto, it pops up:

"An iPhoto update is available. Would you like to open Software Update?"

Then it offers me to start Software Update, but it finds no updates. Some people said I should check in the AppStore, but it asks me to pay if I want to take iPhoto from there.

I am running Mac OS X 10.7.2

I believe this update is to enable Photo Stream.
Have you moved or renamed iPhoto?