Slightly looking over the answers on this error message "We couldn't reach you by email. Please enter a valid email address" didnt give me a proper reason for this message. Some people said that FB or their "frauding policy" is guilty for this, but in my case error was caused by the mail delivery failure.
FB account was registered using "some" mail address. "Some" mail address is double-quoted because website-company that registered my mail has shut down my forum nick and my mail with no reason! Couple of last months weird situations has been going about this internet company and has become a forum topics in community in Serbia. I don't want to write company name because they are total losers, in way of internet reasoning.
Anyway, FB didn't make any mistake( which lots of people says) in my case, got the message "You successfully updated your email address. Please check your email to confirm your new address."
Just changed my mail in FB user panel and sat back on the horse. AAAAAAaaaAAAaaaaaaa