which version of that boards package you have installed(shown in Tools > Board > Boards Manager)
I'd need to know:which version of the Arduino IDE you're using
Select version 1.6.6 and click on Install
As Pert said, problem is an upgrade of Arduino AVR Boards to version 1.6.10. To solve it, you must:access Tools > Board > Boards Managerclick on Arduino AVR Boards (which should show version 1.6.10)Select version 1.6.6 and click on InstallAfter this downgrade it compiles back again.
OK, OK, so the IDE is broken.
Why is this warning not included on the "download" page?
How do I downgrade to boards manager 1.6.9 (which I think i had)?