What version of FCP do you have? You might want use it to export a ProRes clip to see if AE behaves better if you just import ProRes files into it rather than the mts files.
I hear that iMovie Pro -- AKA FCP X -- "optimizes" clips, which is just marketing weasel talk for, "hey, in the background we're transcoding codecs FCP doesn't really like into ProRes". It could be a really fast export from FCPX.
And yeah, this could be part of the Yosemite/AE can of worms. Transcoding to ProRes beforehand isn't only good FCP practice, but it could be a workaround for AE.
There are Mac OSX v10.10 (Yosemite) memory leaks that are not specific to After Effects---but that impact After Effects nonetheless. Do a quick web search for 'memory leak yosemite' to find threads on the Apple community forums with some solutions. The simplest have to do with purging memory within Mac OS (not within After Effects).
Yep - followed all the steps listed here:
Still gettin errors. Any other ideas? I guess maybe this is where I go over to the Apple forums since it's a Yosemite memory thing?