Yahoo "Error 999", A pain in the ass.

Hi all.
Just recently when surfing with Yahoo I get a Page cannot be
displayed "error 999" about every 20 minutes then you cannot log on
again for up to 2 hours. I've heard that Yahoo are using bandwidth
monitoring and when you exceed their limit (whatever that may be) they
disconnect you, hence the 999 error.(I'm not doing anything bandwidth
intensive!) Through Google I heard that Yahoo does this by recording
your IP so I used an IP hiding program and a proxy to access Yahoo
once I'd been disconnected but there was no difference. Yahoo
suggests I may have a virus but that's unlikely because this only
happens with Yahoo and this machine is kept very clean.
Any ideas.
TIA