555 No Such Directory

I'm using Firefox and EVERY time I come to the hompage/any page I open first on this site I get an message:

Alert 555 No Such Directory (in a cute grey box)

I close it down and it occasionally re-appears on this site but I never get it anywhere else. Is it the site, Firefox, my anti virus (which is all ntl broadband medic antivirus and firewall)? Don't have probs with any other sites.

Ok I need to check if Microsift Expolar does it but anyone else have this happen?

noted, thanks for the heads up razorbladesmiles we'll check into it.

Just wanted to add, had to re-format my pc today/last nite just for being an obsessive compulsive who hates having crap on her pc...

Today when visiting the site with IE no error directory messages at all.