Though that's nearly word-for-word what the book says you do when an opponent has total concealment.
I agree that your original comments are in line with a literal interpretation of the two rules in question. What I question is whether they
should be interpreted literally, side-by-side, or whether one should consider the context of each situation.
The invisibility rule is talking about a process by which you attempt to hit a creature that you cannot see. The paladin's challenge talks about what happens if you're attacking someone other than the paladin that marked you.
If someone in our group tried, in all seriousness, to make the argument that in this situation, attacking an invisible creature (generally) didn't qualify as attacking an invisible creature (by the rules), they'd be roundly mocked and their argument quickly dismissed.
Edit: Based on the "What is an Attack" thread, you seem to be determined to treat 4E as if it is a tightly written ruleset that allows you to take only the RAW and extropolate a consistent, obvious and sensible method of play. It seems clear to me that 4E is not written in a fashion condusive to this approach, and insisting on consistent, literal interprations is going to lead to one illogical, unintuitive and unexpected situation after another.
Read generously, for the most part it's an excellent system. Read strictly, it's a mess, and a mess is what you'll end up with.