I have a D-Link DIR-601 (Rev B) router. I’m posting this here just in case anyone else is having trouble connecting their Core to this same model.
I tried every troubleshooting step I could find and couldn’t get either of my Cores to connect to this router. I finally decided not to trust its firmware when it claimed it was up-to-date and hunted down an update on D-Link’s site on my own. So, if you have this router and it’s sitting on firmware version 2.00, you might need to update to 2.01 to get your core working. The firmware update can be downloaded here (make sure it’s revision B, as this firmware update will likely not work with revision A): ftp://ftp2.dlink.com/PRODUCTS/DIR-601/REVB/DIR-601_REVB_FIRMWARE_2.01.ZIP
After applying this update to my router, both of my cores connected instantly and I was finally able to claim them.
In general, if you’re having trouble connecting your Core make dead sure you have the latest firmware for your router if you’ve exhausted all other troubleshooting options.