Take my advice with caution, I'm just trying wild guesses here :
The message you receive from the board is from the firmware itself, you should get it during normal use of the reprap, not during firmware flashing.
I believe something is not working properly to put the board into the bootloader mode - which is the one you should be talking to during firmware flashing.
Usually the arduino software send a reset command before flashing, to reenter the bootloader.
Maybe you should press the reset button on your melzi just before clicking on "upload" ?
If at first it doesn't work try to hold the reset button until the arduino finished compiling - I've seen this operation being sometimes very timing sensitive.
The message you receive from the board is from the firmware itself, you should get it during normal use of the reprap, not during firmware flashing.
I believe something is not working properly to put the board into the bootloader mode - which is the one you should be talking to during firmware flashing.
Usually the arduino software send a reset command before flashing, to reenter the bootloader.
Maybe you should press the reset button on your melzi just before clicking on "upload" ?
If at first it doesn't work try to hold the reset button until the arduino finished compiling - I've seen this operation being sometimes very timing sensitive.