how to solve this problem ?

### Generating code into build folder: C:\MATLAB\untitled_ert_rtw
### Invoking Target Language Compiler on untitled.rtw
### Using System Target File: C:\Program Files\MATLAB\R2016a\rtw\c\ert\ert.tlc
### Loading TLC function libraries
### Initial pass through model to cache user defined code
### Caching model source code
### Writing header file untitled.h
.
### Writing header file untitled_types.h
### Writing header file rtwtypes.h
### Writing header file multiword_types.h
### Writing source file untitled.c
### Writing header file untitled_private.h
.
### Writing source file untitled_data.c
### Writing header file rtmodel.h
### Writing source file ert_main.c
### TLC code generation complete.
### Generating TLC interface API.
### Creating data type transition file untitled_dt.h
### Evaluating PostCodeGenCommand specified in the model
### Using toolchain: Arduino AVR v1.6.1 | gmake (64-bit Windows)
### 'C:\MATLAB\untitled_ert_rtw\untitled.mk' is up to date
### Building 'untitled': C:\PROGRA~1\MATLAB\R2016a\bin\win64\gmake -f untitled.mk all
C:/MATLAB/SupportPackages/R2016a/arduino-1.6.1/hardware/tools/avr/bin/avr-gcc -c -g -w -ffunction-sections -fdata-sections -MMD -DARDUINO=10601 -MMD -MP -MF"untitled.dep" -MT"untitled.o" -Os -mmcu=atmega2560 -DF_CPU=16000000L -DARDUINO_AVR_MEGA2560 -DARDUINO_ARCH_AVR -D_RUNONTARGETHARDWARE_BUILD_ -D_ROTH_MEGA2560_ -DMODEL=untitled -DNUMST=1 -DNCSTATES=0 -DHAVESTDIO -DON_TARGET_WAIT_FOR_START=1 -DONESTEPFCN=1 -DEXT_MODE=1 -DTERMFCN=1 -DMAT_FILE=0 -DMULTI_INSTANCE_CODE=0 -DINTEGER_CODE=0 -DMT=0 -DCLASSIC_INTERFACE=0 -DALLOCATIONFCN=0 -DTID01EQ=0 -D__MW_TARGET_USE_HARDWARE_RESOURCES_H__ -DEXIT_FAILURE=1 -DEXTMODE_DISABLEPRINTF -DEXTMODE_DISABLETESTING -DEXTMODE_DISABLE_ARGS_PROCESSING=1 -DRT -DSTACK_SIZE=64 -DMW_TIMERID=5 -DMW_PRESCALAR=1024 -DMW_TIMERCOUNT=49911 -DMW_SCHEDULERCOUNTER=1 -D_RTT_BAUDRATE_SERIAL0_=9600 -D_RTT_BAUDRATE_SERIAL1_=9600 -D_RTT_BAUDRATE_SERIAL2_=9600 -D_RTT_BAUDRATE_SERIAL3_=9600 -D_RTT_ANALOG_REF_=0 -DONESTEPFCN=1 -DEXT_MODE=1 -DTERMFCN=1 -DMAT_FILE=0 -DMULTI_INSTANCE_CODE=0 -DINTEGER_CODE=0 -DMT=0 -DCLASSIC_INTERFACE=0 -DALLOCATIONFCN=0 -DTID01EQ=0 -DON_TARGET_WAIT_FOR_START=1 -DEXIT_FAILURE=1 -DEXTMODE_DISABLEPRINTF -DEXTMODE_DISABLETESTING -DEXTMODE_DISABLE_ARGS_PROCESSING=1 -DRT -DSTACK_SIZE=64 -DMODEL=untitled -DNUMST=1 -DNCSTATES=0 -DHAVESTDIO -IC:/MATLAB/SupportPackages/R2016a/toolbox/target/supportpackages/arduinobase/include -IC:/MATLAB/SupportPackages/R2016a/toolbox/target/supportpackages/arduinobase/blocks/sfcn/include -IC:/PROGRA~1/MATLAB/R2016a/simulink/include/sf_runtime -IC:/MATLAB/untitled_ert_rtw -IC:/MATLAB -IC:/PROGRA~1/MATLAB/R2016a/extern/include -IC:/PROGRA~1/MATLAB/R2016a/simulink/include -IC:/PROGRA~1/MATLAB/R2016a/rtw/c/src -IC:/PROGRA~1/MATLAB/R2016a/rtw/c/src/ext_mode/common -IC:/PROGRA~1/MATLAB/R2016a/rtw/c/ert -IC:/PROGRA~1/MATLAB/R2016a/toolbox/coder/rtiostream/src/utils -IC:/MATLAB/SupportPackages/R2016a/arduino-1.6.1/hardware/arduino/avr/cores/arduino -IC:/MATLAB/SupportPackages/R2016a/arduino-1.6.1/hardware/arduino/avr/variants/mega -IC:/MATLAB/SupportPackages/R2016a/toolbox/target/supportpackages/arduinotarget/registry/../include -IC:/MATLAB/SupportPackages/R2016a/toolbox/target/supportpackages/arduinotarget/registry/../scheduler/include -o "untitled.o" "untitled.c" 
In file included from untitled.c:16:0: 
untitled.h:24:25: fatal error: rtw_extmode.h: No such file or directory 
 #include "rtw_extmode.h" 
                         ^ 
compilation terminated. 
gmake: *** [untitled.o] Error 1
### Creating HTML report file untitled_codegen_rpt.html
### Build procedure for model: 'untitled' aborted due to an error.
Error(s) encountered while building "untitled":
### Failed to generate all binary outputs.