I assume you meant that you have installed the After Effects 12.0.1 update, not After Effects 12.1 which has not been released yet. The 12.0.1 update is only a compatibility fix for Mac OS 10.9, there are no other bug fixes or changes in the release.
If the QuickTime problem you are experiencing matches what is described here, then the same solutions still apply. In After Effects 12.1, the behavior that causes that problem will be disabled by default, but if you need video preview functionality through third-party hardware you will still risk the problem occurring. In a future release of After Effects the problem will be prevented by using a different technology for video preview instead of the unsupported QuickTime API's that are currently used.
I did delete the DVCPROHDVideoOutput.component but to no avail. In fact an Adobe tech which I gave my computer control to did the deed. He didn't emtpty the trash as your article suggests so I did after his attempts to fix the problem didn't work. I also reloaded QuickTime as your tech suggested. I am still getting the same error message. I guess I am to blame for not researching the potential problems of upgrading to Mavericks. I was using AE CS 5 quite happily up untill Tuesday. Now I can't open that or AE CC. I am dead in the water at the moment.