How did you obtain the GPS, if it's an eBay purchase without an unlock code and of dubious origin then you have a problem. Did it come with the accessories that you wouldn't expect to find in a car or mounted on a bike such as manuals, mains power unit, box etc. If so that's good as it probably indicates that it's not stolen from a vehicle at least.
Did any paperwork come with it that you've overlooked, you're looking for an orange/yellow slip of paper with some serial numbers on it. This is the original unlock, serial number and code for the GPS, it's a sort of provenance.
Contact the seller and ask if he has the unlock code. He might even have registered it with Garmin but thought that unimportant to tell you, if it's registered you need him to inform Garmin that he's sold the GPS to you, they will then, and only then, allow you to register it in your name and set-up a myGarmin account so you can see all the details and previously purchased unlock codes for the associated mapping on-line.
Do you have the NON nt cards installed in Mapsource?, and witch card update do you have (Non NT 2009?).
Good point; To clarify the 2610 runs the non NT mapping, anything later will be running NT. NT stands for new technology, the more recent units have the firmware (and processing power) to use this. NT mapping is stored compressed and is un-compressed on the fly by the GPS as it uses it. The 2610 wasn't designed to exploit this and either lacks sufficient processor power or hardware to cope with the additional overhead.