Hey there,
I was having the same exact problem, but finally got it to work this morning. Here's what I did:
1. Go into Tools >> System.
2. Save your firmware settings to a file and put the file on your PC.
3. Click on the "Restore to Factory Defaults" button. This will completely reset the settings on your router.
4. After the router reboots, go back to the router (mine was still at 192.168.0.1) and log in (the admin password will be blank, just hit the button to login).
5. Go to Tools >> Firmware
6. Upgrade the firmware to the latest version (1.24 if you've got it).
7. Allow the system to reboot, hopefully it will show the version as 1.24 after it's done.
8. Log back in (again, the password should be blank for admin).
9. Go to Tools >> System, reload your settings from the file you made in step 2.
10. The router should reset one more time, and after, you should be good to go.
I did this on a DIR-628 Hardware: A2 Firmware: 1.22NA, which successfully upgraded to 1.24NA firmware.
Hope this helps!