Enter your system lock pin code to unlock this mac

Question

I just traded my Macbook Pro for a 27" Core i5 iMac. I wiped the iMac when I traded and I brought it home to do a full reinstall. I booted holding the Option key down and noticed this iMac had a recovery partition I opted to use the recovery partition to reinstall. To my surprise it was Lion. And the cd was snow leapord.  I was cool with that and signed in and used the computer all day. Then sometime while I was sleeping a obnixious alarm went off on the iMac and there was a box to enter your system lock pin code to unlock this mac.
Priding myself on doing all repairs on my own since my primary job is reinstalled and virus removal. Long story short I could not access anything no matter what I tried. I ended up calling apple care and asking what needed to be done they explained I needed to bring it to a apple authorized store and they would have to unlock the firmware.
Do you guys know what they are talking about or is there anything I can do before driving 100 miles to my nearest apple store. I find this rediculous.

Answer 1

I did indeed did wipe the system clean at the owners house, I went home with what I thought was totally clean hard drive, there was a recovery partition I did not see until I got home. This recovery partition was indeed tied to the original owner which I did not know at the time. I assumed it was like any old windows recovery and it was clean and made reinstalls a dream. Well long story short I had the snow leapord cd in the drive and ready to go until I seen this recovery partition and I opted to use  the **** recovery and I reinstalled registered and signed into everything and used the computer all day 12 hours probably. By the way the recovery partition that was tied to this guy was lion.  
So then I left the computer on and went to sleep. Late last night an alarm went off and that is when I saw the enter the pin to unlock this mac. I have tried holding the C when I boot up, I have tried holding the Option key when booting up. I have tried resetting the pram. Nothing can be done. I can get to another lock screen by phsically unplugging the power cord then booting up holding the option key. That will bring me to a screen with nothing but a lock and a line that I can type some kind of admin password. Nothing I have with work. I tried, root, admin, administrator, my password I used when I set lion up. Nothing!!!!!.
At this point this machine is more or less 100% useless, the only option I can see is to bring it to a authorized apple retailer and have them fix it. I did bring it to a local apple store. And they said they could probably fix it, but I would have to pay them between 50-100 dollars. The repair guy said something about getting the info from the ram. I just laughed and left.
Anyway this is like a BIOS lock, you cannot get to terminal, cd, to any boot options, you cannot reset anything at all. It's a full lock.