It is a long story but this is the short version that has been verified by our server/host.
UP 'at times' is on a black list due to our content. Our host moves us from the black list within minutes of being placed on the list (yes this does cost extra $$$) however, if you sign on when we are on that black list for x minutes, your computer remembers that; Consequently, you get all the warnings.
How you can fix it is to go into your engine and add
UP to your 'okay list' (white list) or when you get the nasty message, click your way through the message (There is usually an icon you can click to get past the warning) and the site will be automatically added to your white list till the next time.
I am sorry that this happens however, it is what it is.