The “Your username and password do not match” error seems to have gained popularity among the Android community. The error is shown when you try to access Android Marketplace from your smartphone or your tablet and no, it’s not you mistyping either of them. Google introduced 2-step verification some time ago, which requires you to enter a code provided by them in order to give a device access to their services, such as Gmail, Calendar, Google+ and others, including Android Marketplace.
If you received this error, the first thing you would want to try is logging into your Gmail account in the browser. As an example, if you just got a brand new tablet and the setup process asks you to add an account, you would not be able to because your tablet is not recognized yet. Just skip over that step, login to Gmail in the browser and confirm your tablet. You should be all set to access Android Marketplace at that point.
If you already have your device set up and started receiving this error, first login to your account from a computer and go to your account settings. In there, you’ll find the 2-step verification settings. The first thing you would want to try is to select Android as the device and click on generate codes. Try using your Gmail email address with one of the codes (as far as I understood, it does not matter whether you include spaces between numbers) to login to the Marketplace.
If the above failed, which is actually what happened in my case, here’s a bit of explanation: my tablet was already registered. That is, before I reset the password first, at which point I started getting errors, and then reset it to factory settings. The reason for that is that Google has your phone or tablet bound to the initial code you used to register it. My guess is that that code is somehow still used when authenticating on Google servers, giving how I factory reset the tablet. So, here’s what you need to do in this case: go ahead and login to your Google account, go to your Account Settings and then click on Edit next to 2-step verification settings. After that, click on “Manage application-specific passwords” and you should see your device registered there. Click “Revoke Access” next to that device, re-enter the name below the list and click “Generate password”. Go back to your device and login using your email address and the password that Google just generated.
You’re all set!