Hello,
the Normal Map warning message behavior in v6.0 is different than v5.0.
Open the scene in attachment and render it with both v5.0 and v6.0.
(*) In v5.0, I don't receive any warning message, since the Bump channel is OFF.
Only when it is on, Corona shows me the warning message.
(*) In v6.0, it doesn't matter if the Bump checkbox is ON or OFF: Corona always show me the warning message
In my opinion, v5.0 has much cleaver behavior.
Is it a bug or is it an internal decision? =)