See the posts toward the end of this thread regarding a memory issue in recent Mac OS, not in After Effects:
You read my other post a few minutes ago.
We UPDATED from MAVERICKS to YOSEMITE last TUESDAY because we WERE getting this issue on MAVERICKS as well. It is NOT a YOSEMITE issue, it is a ADOBE issue as reported by POSTS such as these, that are from NOVEMBER 2013: "Unable to allocate memory" popup on Quit
For the past several days, you have been posting on threads about half a dozen different issues, claiming that they are all the same issue and that we have been "silent" about these issues.
Please, slow down and just start a single thread in which you in detail describe the exact problem that you're having, rather than making accusations and adding links pointing to various different issues. That is the only way that we're going to be able to help you.
Start by answering the questions here about your exact issue: