Hello all!!
I had the same problem with my Arduino Leonardo and my Windows 7. After trying many things, I found a solution.
First: you must find the COMx used for your "Arduino Leonardo" in the "Device Manager" of Windows.
Second: make double click to see the properties of the device, and go to the "Port configuration tab"
Third: enter in "Avanced Options" and deactivate "Use FIFO buffers", and accept all changes.
That is it, now you can program your Arduino Leonardo without the error ..."buffered memory access not supported"
I hope this will be useful!!!! 