I flashed a blank Atmega328 chip with an AVR dragon lended.
That chip was running nicely on the breadboad it had been flashed on.
I could program it with arduino IDE, through a uno board without it's chip.
Then I built a small board for that chip.
The program (blinking LED) is working properly, but I can't reprogram it with arduino IDE anymore.
I got the message :
"avrdude: stk500_getsync(): not in sync: resp=0x00"