You're right! But I don't think the OP, or any player would have that issue when it comes to the legality of castling.
i wonder if anyone has tried though...to castle long with a knight on its original square....
If the knight you are talking about is between the king and rook, then no you can not castle. The squares between the king and rook must be clear.
Post 17! Thank you. Ironically I ran into this yesterday and wasn't sure. I was going to ask. So I can not move my king to say e4 because my opponents knight is attacking it, but what if i have my opponents knight pinned? I still can't move my king to e4?
Remember, (absolute) pinning isn't a rule in and of itself, it is a consequence of the rule that you're not allowed to put your own king into check. If we suspend that rule and let you put your king into check, we have to do the same for your opponent and let them move their knight, which means they capture your king and the game is over ([check/stale]mate is another consequence of not being allowed to put your own king into check, so there would be no checkmates and the game would thus end with the capture of the king).