Wierd black box with x at right top

This black box is a window for videos that appears to have attached to the software at the website somehow. Usually it comes and is temporary. However, hopefully soon it it will disappear. It's nothing to worry about because it is just a video application that allows a small video screen to appear anywhere on a web page for embeded video on that page. But, I'm hoping it is gone soon because likely other bloggers are having the same problem with this defect in the software too.