I have still the same problem, my internet is working perfectly. I use idea 3g network for Xperia U running on Android 4.0.4. I cannot scan the barcode because of whatsapp camera is open in 1/4 of the screen.
I had the same problem, but as mentioned here, basically You just have to move the phone a little to the left or bottom (depending on how you're scanning the code - portrait or landscape).
Hope it works for you too.
Edit: by the way, I have the same smartphone.
Edit 2: I could not make a video because the screen looks completely black, instead of 3/4 of it ¬¬ (ironically, taking a screenshot of the desktop shows 100% of the screen xD). Anyway, what I do is this:
- Open whatsapp and go to the Whatsapp Web option.
- On portrait mode (vertically), center the QR code on the screen (the 1/4 that you see). The idea is to center it like You would without 3/4 of black screen ¬¬.
- Move the phone to the left until I see only half of the squares on the top left and top right corners of the QR code. That's when the code gets scanned.
Hope it helps :)