Thanks to Jazzgirl for letting me know about this problem. I immediately contacted Ash and he got onto the Advert people straightaway. He now tells me the issue has been sorted and everything should be back to normal.
The adverts are an unfortunate fact of life, without them there would be no Forum. However they should not be so intrusive as to make the Forum unusable.
Thank you all for using the Forum, the whole team appreciates your support.