Thanks, yes exactly the error I expect if cygwin can not be located when the toolchain runs

Please put the command in a .bat file and try to understand why it does not work.

"C:\Program Files\Arduino/hardware/tools/avr/bin/avr-g++" -c -g -Os -Wall -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -MMD -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=158 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I"C:\Program Files\Arduino\hardware\arduino\avr\cores\arduino" -I"C:\Program Files\Arduino\hardware\arduino\avr\variants\standard" "C:\Users\montecchil\AppData\Local\VMicro\Arduino\Builds\Blink\uno\Blink.cpp" -o "C:\Users\montecchil\AppData\Local\VMicro\Arduino\Builds\Blink\uno\Blink.cpp.o"

The "CYGWIN environment variable option "nodosfilewarning" turns off this warning." also indicates a similar issue. This is just a wanring that can be ignored but Visual Micro is also setting the envronment variable to prevent this message from happening.

I will also perform some more tests over the next few days but 1.5.8 has been around for some weeks now and there were only two things to make this work for myself and some other testers:-

1) Allow the new g++ to find the cygwin.dll
2) Create a CYGWIN env variable with a value of nodosfilewarning

Thanks

Yes, i found the same article with the gcc error.
Now I solved but i have not undestand how a dll was in toolchain path

Yes, i now.
Buf after this, i have deleted from avr/bin all the dll that was in arduino.exe path and after this the issue is solved.
So, i suppose that the arduino ide upgrade has copy a dll in wrong path, but now i dont know wich of those is

C:\Program Files\Arduino; MUST be in first position of enviroment path (i think because i have winavr installed);

Thanks