RDB was locked at 0xAA and still no erase or flash capability, you need to set again RDP to 0xBB , unplug the board (very important, if not it will not work and stay locked at 0xAA), reconnect to the stm32, you will see RDP with a strange value 0xFF, that is ok, and set back RDP to 0xAA, this time you will be able to change the value.
Today all is ok, I can erase and flash anything 
very very very strange …