This works fine for me:
FRotator ArrowRot = GetArrowComponent()->GetComponentRotation();
Where do you have this error?
If in IDE (but not during compilation), then it’s VS fault as it’s intellisense doesn’t work well with UE4. You may find false errors in editor and stuff like that. I have to use that thing at work, and it sometimes takes couple minutes to show available properties/methods for objects.