It's a D-Link. I don't think I've ever had a D-Link product that didn't become moody, though usually it took 9-15 months for them to get really moody. And I've had routers, access points, and powerline gear from them...
May I suggest returning the range extender (if you can) and just getting a decent router? A condo should be able to be served just fine with a single router/access point, assuming it is decent (i.e. not the Rogers CGN2).