OK,I think I found a solution....
I removed all usb drives and also the xbox hdd drive from the console,except a usb with dashlaunch 3.08 on it.
Cosnole started on stock dash,then used xexmenu (i run it from the internal MU,I have a Jasper 512MB) to launch dashlaunch from USB drive,and it updated fine,asked to update paches and to reboot.
Reconnected all usb drives and the hdd,console booted on FSD3 and runed dashlaunch to verify,3.08 was running!