Arduino ISP Undefined Reference to Main

I am trying to upload the Arduino ISP sketch to my Elegoo UNO clone, and I keep getting the following error:

Arduino: 1.8.5 (Windows 10), Board: "Arduino/Genuino Uno"

c:/program files (x86)/arduino/hardware/tools/avr/bin/../lib/gcc/avr/4.9.2/../../../../avr/lib/avr5/crtatmega328p.o:(.init9+0x0): undefined reference to `main'

collect2.exe: error: ld returned 1 exit status

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.

What does this mean?

This problem has nothing to do with the sketch code. It's some glitch in the compilation process.

Try closing all Arduino IDE windows and then restart the Arduino IDE. That will clear the cache and hopefully solve the problem.