When I entered the code the coin name (printed on the coin) came up, so I know I have the right code. The coin was part of the 10/10/10 event, this one is called "Celebrating Wetlands." I found it in GC16AVM, "Chicago Parks - River."
As requested, here is a picture of the coin with the code blocked out:
I'm guessing this means it's been circulating for the last five years without ever being activated! I'd like to be able to start tracking this little guy if I can figure a workaround to the activation code problem. I'll go back today and check if there was a code in the cache where I found it, but seeing as it appears to have been been around for a while I find that unlikely...