If I try the 'trick' given above (start the printer with panel open, close it after a few seconds) I can access the GUI and swiftly move to maintenance menu. I have a MG6650 since 2y and it did exactly the same: was working well and perfectly printed a set of photos for Christmas and now I get a B203 error right after I start the printer. Sounds simple yes but I just followed my gut feeling. You can do a few more maintenance checks if you want to keep your printer in mint condition. Once done it will print a test page and tadaaaaa! it works. And start the process let it finish and follow any instructions it may ask. Next go to settings/ maintenance settings / auto head allignment. Now if you try to print anything the error might come again in which u repeat the steps above. Wait a minute or two and you should be back to normal menu. Now turn on the printer wait till the ink head starts moving a bit then just shut the cover back to normal. While the printer is off, open the front cover where the ink is. So to summarize it in short follow these steps and you may be as lucky as I have. I simply could not throw my MG 7540 Pixma just like that. If such a warning message appears, set the security software to always allow access.So I just want to post my solution finally after a while of trying some of the solutions on the internet and none worked for me. If the firewall function of your security software is turned on, a warning message may appear that Canon software is attempting to access the network.The installation resumes once your computer has restarted. Follow the on-screen instructions and do not remove the Setup CD-ROM during restarting. It may be necessary to restart your computer during the installation process.Internet connection may be required during the installation.Do not switch users during the installation process.Quit all running applications before installation.Log on as the administrator (or a member of the Administrators group).

(The installation time varies depending on the computer environment or the number of application software to be installed.) The installation process takes about 20 minutes. To use the machine by connecting it to a computer, software including the drivers needs to be copied (installed) to the computer's hard disk.

Pixma 439 manual