Kernel panics; Apple hardware test error codes... Bad memory? My MacMini, which I bought new around Thanksgiving 2010 from Amazon, has been having quite a few kernel panics. They aren't consistent in any way, but they have become more frequent and now many apps seem to be crashing more as well and I have also noticed Spotlight and Alfred have become painfully slow.

I was about to reinstall Snow Leopard and start from scratch after making a SuperDuper clone on an external for backup when I read on the Apple CD that you can run an "Apple Hardware Test" by holding "D" during startup.

I figured it was worth checking out. Especially since my memory is non-original. I had put 2x 4GB Corsair sticks in it right away that I also got from Amazon a few months before then which I had used in my previous early-2009 MacMini. The memory seemed to have worked fine in both computers. All 8 GB were being recognized. These kernel panics only started happening a few months ago.

Now the Apple Hardware tests, which I tried in every conceivable configuration; swapping slots, removing one then the other etc., did in fact show errors. I wrote down two of the error codes. I believe there were only two unique codes; I suppose the different stick arrangements I used is cause for the variances, but it's possible there were more, but I know for a fact they all started out with the same characters, 4MEM/9/40000000: .

4MEM/9/40000000: 0xa90c1418 &amp; 4MEM/9/40000000: 0xa95de698

However, the strange thing is the Apple Hardware Test only showed this error when I had BOTH sticks installed; either stick in either slot on it's own showed no error. As I mentioned earlier, I tested all possible configurations because I had read that sometimes it could be a faulty slot.

So, with that information, does anyone have an idea how to fix my Mac. Do I need to replace one or both sticks? Is it something else? Is there an app I can use to help diagnose the issue?

As I'm writing, I realized I can still try using both the original sticks that came with the Mac at the same time, but I need to find them. I may wait until tomorrow to try that.
It sounds like some sort of RAM issue for sure, and there are a few memtest based programs out there to try and run and see if you run into problems.
Rember is a gui based memtest, and applejack is a fairly well known utility script that also contains it.

I dont know why you only got the error with a specific configuration of ram, but with 8GB of addressable space it can take a while to find the bad guy.