in 1.6.6 version on select genericesp8266 board
Invalid library found in C:\Users\maxid\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\1.6.5-1160-gef26c5f\libraries\esp8266: C:\Users\maxid\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\1.6.5-1160-gef26c5f\libraries\esp8266