I am using IDE 1.6.9. and after updating Arduino AVR Boards to v. 1.6.12, I can no longer upload to board. Going back to v.1.6.11 and it works again.Tried this on Arduino Mega2560 and Nano. Same result.Any idea? i have just bought arduino products from http://www.w11stop.com/arduino-mega-price-in-pakistan