For those of you receiving this error message, just wondering, do you already have an Explorer card?
I have noticed that, the Reserve card is categorized as 'Reserve or Explorer card'. Don't know if the system is 'smart' enough to find that you have already have a card in that category. Just a guess.
Also, worth well to double check with them to confirm there is no hidden card under your account. Previously, people reported that one of their old card was converted to another type of card, which he didn't aware of. Thus, creates problem for new card application.