When I first get to the Forums,I get a pop-up that just sits there with nothing on it and won't let me do anything sept wait with my thumb in my ass. Then when I can finally do shit again,whenever I post or look at a topic,I get that "error has occured in the script" shit every time a new page loads.It's chapping my ass I tell ya..
Try this: When the ad comes up, and it hovers in the background, click on the box in the taskbar that corresponds to it. Then, hold down Alt and hit F4 once. That's a shortcut for the 'close window' choice on the right-click menu that seems to be disabled on that particular ad. You can also use that same sequence to bring up the 'shut down' menu if you have no windows 'up' at that particular moment.