Visual Studio Error List isn't any helpful

Open the output panel ( View → output / Ctrl W → Ctrl O )

Error list in nor reliable, output log tell you what compiler say ( much better to fix errors )

in your case, as you said you want to find all cameras : i would suggest to use the actor iterator feature :

for (TActorIterator<ACameraActor> It(GetWorld()); It; ++It)
		{
			ACameraActor* camera = (*It);
		}

Also,you don’t have to cast to correct class when you try to compare 2 Actors ( or UObjects ) because you are comparing pointers, so it would be perfectly find to do

if(OurPlayerController.GetViewTarget() ==cameras[i])
{
// some code
}