photos lost, appear in "last import" ...

Thinking that it would be a shortcut, I used "Open With" on some photos I had in Finder to open them in iPhoto. It worked and they showed up in iPhoto as an Event. However, when I click on an individual photo it enlarges as usual, but then a window pops up that says "Alert: the photo _____ could not be opened, because the original item cannot be found." It gives me two options: Cancel or Find Photo. When I click on "Cancel", the photo is replaced with a large exclamation point. When I click on "Find Photo", it takes me to Finder where the photos are no longer located -- they have completely vanished. What on earth happened?

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Orignal From: photos lost, appear in "last import" ...