Compiling fails as soon as I add a second UCLASS!?

Thanks for the tipps! I changed all “int” to “uint8” and “int32” and put an F in front of the struct name. The Ustruct works fine, now! Thanks.
And yes you are right, it doesn’t make any sense to derive from UBluepritnFunctionLibrary with my new class. I just ended up trying this, because a few lines above the exact same code works… so i thought, maybe it works if I make it the exact same.
Ok, I now derived it from AActor and put an “A” before the name. But I still can’t get the class to compile.

UCLASS()
class AArtNetUDPReceiver : public AActor
{
	GENERATED_UCLASS_BODY()
};

Still the same error. I also tried to derive from UObject and put an"U" before the name:

UCLASS()
class UArtNetUDPReceiver : public UObject
{
	GENERATED_UCLASS_BODY()
};

The same. Any Idea?