IDE 1.8.0 and previous versions, stopped compiling for UNO R3, same code used to compile

Question

Arduino: 1.8.0 (Windows 10), Board: "Arduino/Genuino Uno"

c:\program files (x86)\arduino\hardware\tools\avr\bin\../lib/gcc/avr/4.9.2/../../../../avr/bin/ar.exe: unable to rename 'core\core.a'; reason: Permission denied

exit status 1
Error compiling for board Arduino/Genuino Uno.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

Answer 1

In my case, the same error was produced by antivirus detection.

I can suggest two tests:

1. Run Arduino IDE as Administrator (again, just for testing!)
2. Exclude directories (or filetypes) from searching / testing in your antivirus tool