Missing Library?

Arduino: 1.8.9 (Windows 7), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"

ECDSA_test2:28:20: error: common.h: No such file or directory

compilation terminated.

exit status 1
common.h: No such file or directory

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

@RavKal, yours is a completely new question in a very old Thread so I have suggested to the Moderator to move it to its own Thread.

You need to post the program that is giving rise to the error.