I also bricked my Linksys by opening /upgrade.cgi (mentioned in the article) on a browser.
I was able to finally fix it by downloading a firmware from Linksys, doing a 30/30/30 reset (push reset button for 30 s, turn power off for 30 s and keep on pushing reset for another 30 s after turning it on again) and flashing it with tftp as explained in http://community.linksys.com/t5/Wireless-Routers/E4200-Firmw...
After that I was able to login using the web interface again.
For Mac OS X the command to flash is just tftp, and then in the console that opens type:
connect 192.168.1.1
binary
rexmt 1
timeout 60
put firmware_filename.bin
I was able to finally fix it by downloading a firmware from Linksys, doing a 30/30/30 reset (push reset button for 30 s, turn power off for 30 s and keep on pushing reset for another 30 s after turning it on again) and flashing it with tftp as explained in http://community.linksys.com/t5/Wireless-Routers/E4200-Firmw...
After that I was able to login using the web interface again.
For Mac OS X the command to flash is just tftp, and then in the console that opens type: