fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364140 .. there are also invalid public keys. The reason is there are pub keys that lie outside the curve. But i gotta agree that the mentioned pubs above are interesting, especially knowing that one of their addresses is a used one.
There is no such a thing as invalid private or public key, whatever private key you think is invalid or outside the range, I will prove you wrong if you just show it to me.
Deal! Prove wrong, type this pvt key into the "view details" page in bitaddress.org and if you get an address out of it I'll send you 5 BTC:
fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364142