I followed steps provided to build RRF3.3(Duet2) at https://github.com/Duet3D/RepRapFirmware/wiki/Building-RepRapFirmware
I can't build RepRapFirmware in following error.
Do you know what's wrong?

Projects :
CoreN2G 3.3-dev SAM4E_SDHC
FreeRTOS 3.3-dev SAM4E
RRFLibraries 3.3-dev SAM4E_RTOS
RepRapFirmware 3.3-dev Duet2
DuetWiFiSocketServer dev

USARTClass.h was nowhere to be found on my computer.
So I tried importing CoreNG into eclipse, but the same error occurred.
Please advise.