I am having the same problem, except reinstalling the drivers did not fix my problem. However, I may have another issue as well. This all started after I installed the motor control server (http://www.mathworks.com/academia/ardui ... atlab.html
). I have the server uploaded on the arduino and was just messing with the motors through MATLAB. Now, whenever I try and upload any sketch onto the arduino board through the IDE, I get the same error as the poster. The weird thing is I can still talk to the arduino through MATLAB, such as sending values and reading data to the motors. The TX and RX lights light up ONLY when I connect through MATLAB. I can not get them to light up whenever I try and upload a sketch to the board through the Arduino IDE. I have the Arduino Mega 2560.
Thanks in advance