Upload problems

I have an Arduino Leonardo on both Windows XP and Windows 7 platforms, it was working properly until an hour ago. I wrote up a sketch, I tried to up load it. I had the error message below:

Binary sketch size: 4,826 bytes (of a 28,672 byte maximum)
Found programmer: Id = "BOL"; type =
avrdude: error: buffered memory access not supported. Maybe it isn't
a butterfly/AVR109 but a AVR910 device?

and LED (pin 13) along with the power LED is on and LED does not blink or turn off.

when Arduino is reset and reconnected to the computer, the bootloader works, computer recognizes Arduino and the prior sketch that was stored in the memory starts working, normally. When I tried to upload another sketch above mentioned error happens, again.

I looked up for this problem, in the forum. It says: bad cable or wrong serial port number. I tried different cables, different USB ports on computer and different computers, problem didn't go away.

I tried loop back test, during the loop back test when connected to the computer, windows can not find Arduino, nothing happens and LED (pin 13) and power LED is on and does not turn off.

I can't explain what's going on. Can anybody help me?