compile error message with Arduino Uno

I have Arduino Uno loaded on both a Windows PC and a MAC (OSx). Programs were developed on the PC and run fine. When I try to verify a program which uses an Ultrasonic Module HC-SRO4 on the MAC, I get the following error message: 'NewPing' does not name a type. The program runs fine on the PC. I would greatly appreciate any help. Thanks, Ed

The program runs fine on the PC.

Where the library is installed, but not on the Mac where it isn't?