Dear RoadStar,
If you search the code base you will find TriggerBox.h, so its definitely there 
/** A box shaped trigger, used to generate overlap events in the level */
UCLASS(MinimalAPI)
class ATriggerBox : public ATriggerBase
{
GENERATED_UCLASS_BODY()
**Include**
Try adding this include to your .h file, above your .generated #include!
```
#include "Engine/TriggerBox.h"
```
Let us know!
:)
Rama