Answer by Graham Dunnett

The error message says it's line 43 of your HealthBarJava.js. And that it's inside the OnTriggerEnter() function. Your OnTriggerEnter() function only has two real lines of code. Line 43 is using your `damageScript` variable. Nowhere in your code can I see you check if that variable is assigned. Your line 4 looks it up, but how do you know it's been found? Probably worth checking that.