When playing oblivion I get blue lines at the edge of the screen like in every side. The top edge and left and right and left. its a long line. But it dissappears when i enter a building but when i'm outside Its back?

Are you forcing AA?

Just bumping this to thank you Thomas. I was having the same issue as Ace with a blue line on the left edge of the screen as well at the top. AA was not turned on in the game but it was in Catalyst Control Centre. Disabling that fixed the issue.

It's true, the blue lines are caused by having AA enabled.