Hello,
I have the same problem: http://forums.dlink.com/index.php?topic=65347.0
I'm from Germany, if that's important. ISP-information is not I guess:
Router worked totally fine until I upgraded the firmware from 2.11 to 2.18 on the DIR-600 H/W: B5.
The name of the zip containing the update: DIR-600_fw_revb5b6_218b01_ALL_de_20150424.zip
Now it says the standard user/password combination is incorrect after several factory resets (meaning: "admin" as a user and "" as a PW).
On Linux and Android it says the CAPTCHA is wrong, but I can't see any field to input a CAPTCHA.
If I use Noscript and deactivate script + style I can see that CAPTCHA is deactivated in the options (though I'm not able to make any changes to the options, maybe the option isn't even loaded, so maybe in fact the CAPTCHA is activated?). If you use Noscript like this you can freely browse the settings like as if you were logged in.
I tried pretty much every user/password combination coming to my mind and nothing works. "blank" written-out also doesn't do the trick.
Now I have an open WLAN which is simply dead.
What am I doing wrong? I just did what the installation instructions said:
connted via wire, delete language setting, save config, install firmware, deleted settings via factory reset.
Browsers I tried: Android: 6.0 standard browser, Debian: IceWeasel, Windows: Chrome, Firefox, even IE.
And: The connection via 192.168.0.1 is tricky. Most of the time it only works via wire. Before updating the router had 192.168.0.11 as an IP, set by my modem.
After updating that didn't work anymore, although it should I guess, since it was in AP-mode. What changed there? I don't know.
Long story short, TL; DR: The default blank password does defintely not work.
What to do now? Please help.
Btw.: The Noscript-"hack" let me install the language pack for 2.18 even though I was not logged in.