I too am having issues with Prores Quicktimes rendered out of After Effects CC, as they are not usable and crash in Final Cut Pro 7.
I believe that this is due to Adobe CC products using a Adobe Prores Codec that is not compatible with FCP 7.
Note: Files rendered with CS6 apps work fine as those are using OSX (Apple) codecs which are compatible with FCP7.
Also, the Adobe CC and FCP 7 are on two different machines. One in a graphics dept (OSX 10.8). and the later in editorial dept (OSX
Current solution is to re-process the rendered Adobe CC .mov in Apple Compressor or Quicktime 7 Pro, FCP 7 only likes the Apple codec it seems.