Different Apple ID in app store?
I have had my macbook white for three years now and I recently updated it to OSX Yosemite. I saw that iPhoto wasn't working so I went to update it in the app store. Now, I have been using the same apple id for the app store, itunes etc. in all the time that i have had my laptop. After signing into the app store with this apple id I have always used, I went to update iPhoto. However, when I clicked update, the app store wanted me to sign in. This was strange since I was already signed in, but what confused me even more is that the email address it wants me to sign in with is one I have never seen before and I do not know it's password, and the app store is not letting me enter my own apple id. This is making me really annoyed since all I want to do is access my iPhoto and the thousands of photos I had stored on it before the update. So my question is: How do I get rid of this random email address to be able to use the one I have been using for the past 3 years? Thanks to everyone that replies.
MacBook, OS X Yosemite (10.10.1)