RAW conversion no longer works for my Olympus E-PM2 since I updates to this version.

I'm relieved that I'm not the only one that is having this problem. I'm having it for my Sony RX-100. I don't have a solution, but I've played with it enough to get around the problem some of the time. What I do is crop the photo that has converted wrong, move on to the next few photos, but don't do anything to them (unless you hit a good one in which case I always edit it because I don't want to risk having it fail later). Then I eventually go back to the one that failed and I Revert to Original. About 80% of the time the resulting original is fine and I can work on it.

Of course this workaround is unacceptable for the amount of time I'm wasting, but at least I've been able to use some great shots that I needed.

I can import ORFs from an E-PM2 successfully into Aperture 3.6 in Yosemite. No problems. And they display correctly in any other application that relies on Apple's raw converter, including eg QuickLook. Have you tried QuickLook? If that works, it's Aperture, not the raw converter itself. If NOTHING can show that RAW (some applications, like Lightroom, use their own converters, not Apple's; Pixelmator would be an example of something that uses Apple's), then you might have to delete the converter and download it again.

Have you tried iPhoto or Photos? they use the Apple raw converters too.

If it's Aperture, I dunno what you do. It's harder to even find forum support for it now, and to be honest I can't remember if a pref delete or reinstallation would help or make things worse.