400 Bad Request Request Header Or Cookie Too Large

Hello VinceGreco,

We'd love to assist you with resolving the error you are receiving. Can you tell us what you are doing on your Mac when you receive the error? Are you trying to access a specific website in Safari? If so, does the error appear as a pop-up or is it only appearing when you try to access a specific website? You can find some helpful tips to resolve pop-up ads and windows in Safari here: About pop-up ads and windows in Safari

Take care