ArduCopter Linking error

Hi All !
I am getting a linking error while running ArduCopter SITL on Ubuntu 16.04.

[533/533] Linking build/sitl/bin/arducopter
ArduCopter/ArduCopter.cpp.27.o: In function Copter::ten_hz_logging_loop()': ArduCopter.cpp:(.text._ZN6Copter19ten_hz_logging_loopEv+0x12d): undefined reference toAC_PosControl::write_log()’
ArduCopter/Attitude.cpp.27.o: In function Copter::set_throttle_takeoff()': Attitude.cpp:(.text._ZN6Copter20set_throttle_takeoffEv+0x8): undefined reference toAC_PosControl::init_takeoff()’
ArduCopter/GCS_Mavlink.cpp.27.o: In function Copter::send_nav_controller_output(mavlink_channel_t)': GCS_Mavlink.cpp:(.text._ZN6Copter26send_nav_controller_outputE17mavlink_channel_t+0x89): undefined reference toAC_PosControl::get_alt_error() const’
ArduCopter/GCS_Mavlink.cpp.27.o: In function GCS_MAVLINK_Copter::handle_command_long_packet(__mavlink_command_long_t const&)': GCS_Mavlink.cpp:(.text._ZN18GCS_MAVLINK_Copter26handle_command_long_packetERK24__mavlink_command_long_t+0x530): undefined reference toAC_WPNav::set_speed_up(float)’
GCS_Mavlink.cpp:(.text._ZN18GCS_MAVLINK_Copter26handle_command_long_packetERK24__mavlink_command_long_t+0x6c1): undefined reference to AC_WPNav::set_speed_xy(float)' GCS_Mavlink.cpp:(.text._ZN18GCS_MAVLINK_Copter26handle_command_long_packetERK24__mavlink_command_long_t+0x711): undefined reference toAC_WPNav::set_speed_down(float)’
ArduCopter/mode_althold.cpp.27.o: In function `Copter::ModeAltHold::run()’:

I checked make.inc and AC_PosControl and AC_WPNAV are included in the Libraries field. Please share your recommendations if anyone have come across similar issue.

Thanks,