This keeps happening to me! Scanned PC it's not spyware or anything my end. Windows Was fresh installed Last week from a genuine Microsoft 8.1 ISO. Just did a scan for anything in case and yep PC is clean.
If i refresh the page the advert will go and i can browse the site as normal.
I have had to resort to blocking adverts on this site now. Figured i would bring it to your attention just in case i am not the only one.