If you are 200% sure the tried, proven, and working by others besides you. You may forget to refresh you Arduino Development Environment. case 1: in your sketch code: #include "?????.h" rather than #include should be used case 2: you have started your Arduino Development Env. Later, you added a new library folder under your Arduino directory you then test the sketch codes, and found "error in ???.h" >> You must close the Arduino and add the library first, and re-start Arduino to take effect