SOLVED: Strange phenomenon with avrdude: stk500v2_ReceiveMessage(): timeout only with ATmega250 on windows 7x64
I found the problem coming from a mismatch of the port speed setting and the baudrate in the avrdude command.
It seems that the ATmega is very sensitive to timing issues.
After I did set everything to 115200 it works on my w7 box like on the notebook.