The Arduino IDE version 1.8.5 gave the same error every time I tried to connect it to my OSEPP Nano. I tried it on Windows 10, and on Mac OsX with 2 different Nano's and also tried rolling back to 1.8.4 on the IDE. The serial loopback test passed also. I had the board set to "Arduino Nano", and the processor set to ATmega382P. I ensured the correct port was set because I could see the new port show up and disappear when I plugged in the Nano and removed it. I am using the USB mini connector in the Nano.

The solution was: Choose the Arduino/Genuino Uno and it worked!

Someone needs to fix this so that selecting the Nano board works with the Nano

The Arduino IDE version 1.8.5 gave the same error every time I tried to connect it to my OSEPP Nano. I tried with multiple nano boards with different versions of the IDE. I had the board set to "Arduino Nano".

The solution was: Instead of Nano choose Arduino/Genuino Uno. This worked for me.