If in your ProntoConfig.ini file you have the "IPCheck" setting turned on, all inbound requests checked to see if their IP address is listed on the dynamic block list, and deny access if it is.  Participants that fail their authentication may trigger this security access block functionality as well.  If IP addresses or process Participants show up on this list, you may click the delete icon to remove them from further access blocking.

Note: this screen will only display for System-Wide Admins and it not Account or Group specific.