Can't install Arduino Mega2560 board support package using Target Installer

I am trying to install the Arduino Mega2560 board support package using Target Installer on a Windows 7 64 bit machine and MATLAB 2012a/Simulink.

When I get to the downloading and installation part, I always get an error message along the lines of "Arduino Mega 2560 hardware target information file rtt_arduino_mega_2560_info does not exist" (My computer is in the Japanese language so this is a translation)

I have tried to install using both the Internet option and the Folder option where I download the support package first. I have tried to install other support packages - Beagleboard and Legomindstorm - but I always get similar error messages. i have tried Arduino Uno without any change in luck.

Interestingly, I have come across only one other person on the entire web who also faced such a problem.

Does anyone have any ideas on how I can resolve the above error? Would be much appreciated!