Hi, I also have the same problem.
I bought a new MacBook Air and now I have all kinds of trouble unfortunately. I had a time machine backup on an external HD. So I opened the new Macbook, chose to use the backup from the HD, and then most things worked immediately. My two biggest problems are unrelated to each other. First the issue that is discussed in this group:
After I imported all my stuff from the time machine backup, my MacBook says I can't open iPhoto anymore because it's not compatible with Yosemite. I notice that I can access my photos through the Photos app, which I've never seen before. However, they can't be opened in Finder, which is a little annoying, because I have 13.000 photos and 368 videos, and I want to select all videos and copy them to a USB-stick for my parents... I can't even easily locate them now. Unless I scroll through ALL 13.000 files... Would my problem be solved by 'fixing' iPhoto somehow?
My other problem is that I also transferred my mails to Mail of course (with the time machine backup). Seemed to work. I have a sent-mail folder on IMAP, and I have one 'On My Mac', which is locally stored. That last folder had 97.000 e-mails. Full archive since 2003. I opened it in Mail, worked fined, until suddenly the folder was empty. I didn't do anything: I was reading an e-mail and boom... all gone... It's the only folder that's empty now. If I go to time machine to get a back up back, it loads all messages (which I can see in time machine then), but when I click restore, nothing happens. Well... yeah... the screen freezes... only cmd option escape gets me out of the screen... how can I fix this..?