Thanks for the info. We don't normally support the nightly Arduino build because it can contain yet to be released changes that we need to cater for. In this case the build is OK, we tested it. 

When an Arduino and a VisualMicro build happens, we are actually just running the various tool chain EXE commands to build files. We can see that you system has failed on the very first file it attempts to build. 

The build command takes the path to a source file, in this case "wiring_pulse.S" and outputs as "wiring_pulse.S.o" into the temp build folder.

This is the build command that fails for you. You can paste this command into a cmd.exe prompt and should see the same error. I think it means your virus checker or some permissions is interfering with the attempt to create a file.

"C:\Program Files\arduino\arduino-nightly\hardware\tools\avr/bin/avr-gcc" -c -g -x assembler-with-cpp -flto -MMD -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=108013 -DARDUINO_AVR_UNO_WIFI_DEV_ED -DARDUINO_ARCH_AVR -DESP_CH_UART -DESP_CH_UART_BR=19200 -I"C:\Program Files\arduino\arduino-nightly\hardware\arduino\avr\cores\arduino" -I"C:\Program Files\arduino\arduino-nightly\hardware\arduino\avr\variants\standard" "C:\Program  -o 63748e2\core\wiring_pulse.S.o"   

The Arduino IDE executes the same command but it uses java instead of C# which is why there can sometimes be differences around permissions and virus checkers.

Can you please confirm if the command does produce the same error when run via cmd.exe

Thanks

Thanks. You missed the double quote " at the start of the avr-gcc command.

Please copy/paste my example again into cmd.exe

Thanks