i updated all of my sites the other day and now have the error "The webmaster has forbidden your access to this site" when logging on to jooomla but i can log on and get access. A 403 error is displayed to the normal user on all pages. Disabling the securitycheck pro firewall fixes the issue on all sites which ive done for now to restore access. Ive tried defauting the securitycheck pro config and also tried chossing just the easy config with no luck. Strange but i thought that ihad tersted the sites after i upgraded but it seems they have been off line since Thursday !
That message means that the IP trying to access is blocked; if that happens to all users maybe there is something like *.*.*. into blacklist. Can you check it?