Which version of Bridge/Photoshop are you using? ACR 6.4 only works on CS5 (and besides, you are better off with ACR 6.7.1 on CS5).
I am using CS5 (CS 5.1). The issue is that when I switched to my new camera and set it to shoot in RAW, I can't open them in PS or Bridge. Raw images from my older Nikon allow me to open them through Bridge into this box, which I can quickly edit them. This is how I have learned to do most of my editing, and this is how I prefer to do it. But my new camera (Nikon 5200) isn't supported by the old version that I currently have. When I try to update it, it gives me the error code I mentioned above. (Also I am using a PC, not a Mac.) Is there anyway you (or someone) can help me get this updated?
The D5200 wasn't supported until ACR 7.3, which will not work with your CS5. You would need to upgrade to CS6/CC to be able to use a version of ACR which will open D5200 files.
Alternatively, you can use DNG Converter 9, which is free. This creates DNG copies of your NEF files which can be opened in ACR 6.x for CS5. Make sure its compatibility preference is set up correctly. I still recommend updating ACR to the last version for CS5, which is ACR 6.7.1, available from the Downloads section of the Adobe website. You get all the latest features and bug fixes.
Another alternative, which isn't free, is to use Lightroom to convert your Raw files. It's a lot cheaper than CS/CC. However, you might prefer to subscribe to the Photoshop/Lightroom version of CC, which I am told isn't as expensive as one might think.