Well, upgrade to 1.6.9 gave me different error message:
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x18 avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x66 avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x66 avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x1e avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x06 avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x98 avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x98 avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0xe6 avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0xf8 avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x06
downgrade to 1.6.6 gave me this:
avr-g++: error: missing filename after '-o' exit status 1 Error compiling.
downgrade gave me the same error I had with 1.6.8
avrdude: no programmer has been specified on the command line or the config file
Specify a programmer using the -c option and try again*
Some of these errors apear even when I try to upload the code with board not connected to USB so I guess it's the matter of some IDE setting
The problem is caused by using Arduino AVR Boards 1.6.10 with Arduino IDE 1.6.6, they are incompatible. The options to fix this are:
Use Arduino IDE 1.6.7 or 1.6.8
Install Arduino AVR Boards 1.6.8(due to a bug you can't go back to using 1.6.9) by: Tools > Board > Boards Manager... > Arduino AVR Boards(click on it) > Select version > 1.6.8 > Install.
Install Arduino AVR Boards 1.6.9 and then reinstall Arduino IDE 1.6.6, this will get around the bug linked in option #2.
With option #2 or #3 you will continue to get updatable notifications about the more recent Arduino AVR Boards version so you might want to File > Preferences > Check for updates on startup(uncheck) to disable this notification.
At first I thought the instructions did not work, but as it turns out, it instead appears like some combination of changes bricked my Arduino Nano. Luckily, I have another and that one will upload sketches successfully using IDE 1.6.9 and 1.6.8 boards although this results in WARNINGS: Category '' in library {EEPROM,SPI,SoftwareSerial,Wire} because the old core being used.
One of my students had this same problem and was using Arduino AVR Board version 1.6.11 (Arduino IDE 1.6.7). Downgrading to 1.6.10 resolved the issue for him.
I have been using 1.6.7 for some time now, both before and after Win 7 Pro to Win 10 Pro updgrade.
Uploading etc. worked fine up until a few days ago, then the problem described started with no changes on my part.
Before finding this article, I had to resort to a clean install of 1.6.11 to get things working again.
The only thing different in working practice was more projects involving bare 328PU chips and a Sparkfun FTDI adaptor. The problem had never happened before over quite a few years of using Arduino