Apple Hardware Test Error: 4MEM/66/40000000: 0xa83a0f18

I have a Mac Mini (mid 2010) with Lion installed. Everything has been updated with Software Update. This Mac was bought new and the stock memory has never been changed. I have had the computer since 2010, but the problem (below) has only been happening for the past 6 months.

Here's the problem: I have been receiving the following msg.

This occurs both while I am working on the computer and while I am away from the computer. It happens almost everyday that I work on my computer; sometimes multiple times a day.

The 1-year Apple warranty has already expired so I have been trying to troubleshoot this myself.

To be sure that it wasn't software or peripherals, I erased the Hard Drive and reinstalled Lion anew. While I was transferring some backed up files from my external Hard Drive, the above error message occured already (this was within 5 minutes of cleanly reinstalling Lion & no other peripherals were attached).

I found the Apple Hardware Test so I ran an "Extended" test and received the following error:

4MEM/66/40000000: 0xa83a0f18

I've been assuming that this "Restart your computer..." error message is a kernal panic related to faulty RAM. Does the following error message from the Hardware Test confirm this? If not, can somebody please advise me what this error signifies? (Google does not show any results for it)

Could it mean the actual RAM slot is defective?

Any other troubleshooting directions?