Just installed Mavericks and iPhoto doesn't work!

"You cannot open the application iPhoto because it is not supported on this type of Mac". That is the message that appeared when I tried to open iPhoto. Now what?! I was running Snow Leopard, did an update last week, and did a back-up today before installing. Do I need to get the new iPhoto? If so, why didn't that come up as a warning before I installed Mavericks??? (Like the warning I got about Microsoft Word, which I really don't use anyway...)