I have the same problem in iMovie. Plus iTunes also can't access iPhoto library so it can't sync photos to my iPads & iPhone. The problem started after Mavericks upgrade / new iPhoto version upgrade.
In both cases in iMovie and iTunes trying to access iPhoto library creates just infinite spinning "sun rays" like symbol. The longest wait I've tried is 10+h so it seems it´s stuck permanently.
iPhoto works still OK. The libraries for iPhoto and iTunes are shared as afs by a Mac Mini and I'm accessing it from my Macbook Air.