downloading a program to de board!!

hello everybody!
I wanted to download a program on the Arduino board, but I had the following error:
::
avrdude:stk500_getsync (): not in sync: resp = 0x30
avrdude: stk500_disable (): protocol err : or, expect = 0x14,
resp = 0x51.
::
I have an aduino: Duemilanove ATMEGA328p-pu
… I will signal that there is already a program on the board (it works well) … I do not know what is the problem!! Somebody can help me? :frowning:

Do you have a 64-bit computer? The arduino IDE does like 64-bit for some reason.

Hmm... have you got a shield attached?

I think I've seen sync errors when certain shields have been plugged onto the Arduino during program upload.