Which bootloader have you installed ?
the bootloader shipped with the arduino IDE for the MEGA 2560 is not watchdog compatible. If you want to use the wdt you have to install an alternate bootloader with a programmer
Which bootloader have you installed ?
the bootloader shipped with the arduino IDE for the MEGA 2560 is not watchdog compatible. If you want to use the wdt you have to install an alternate bootloader with a programmer