The message implies that your IP address, or perhaps a range of addresses including your IP address, has been banned from accessing a particular site. Sometimes that could be caused by detecting an attack from that/those address(es), and in other cases by a history of spam from an address. Sometimes an IP address may be out of the geographic service range of the site. Or perhaps it is simply that your address is not on a preapproved list, if the site is very strict. By "your" IP address I mean the one currently assigned to your connection by your service provider. If you are using a VPN, then your address was assigned by your VPN service, otherwise it's usually the service to your current location (e.g., cable, DSL, wi-fi hotspot, etc. ). Could you explain where you are signing in? Is this problem on the Mozilla Add-ons site, or is it on a non-Mozilla site used by an extension?