Human verification is neccesary thanks to excessive automated download attempts of the entire site as well as Google Safe Browsing falsely labeling RHDN as a malware site in the past.
If you are sure the password was entered correctly, your browser configuration may not be allowing persistent sessions. Make sure you have cookies enabled. Try disabling any anonymization add-ons or proxies in use. If you still cannot meet the criteria for guest downloading, you will need to register for an account.
