Most people would have to see a live link on forum on this issue as it could be anything. You could have some custom css that is doing it but without a live forum no one can help. Picture does no good. Usually border = 0 or if you are using CSS then border-style =none;
I had this problem as soon as I moved to VB4, so I didn't have any template modifications or custom CSS and I don't have it live because it is very ugly to have it on my board.
Then you have the wrong div you are applying it too. Since this is not a live forum you probably will not get this solved til it is live. You know you can have a live forum and testing forum online. That is not against the rules at all. You just can not have it linked anywhere . Usually password protect it also.