I thought I had a variant of this when I went to Yahoo Maps and got a blank page with a URL which ended in ?env=#F. Ran a full Trend Micro scan, which specifically lists the red.clientapps as something it can fix, but it didn't find it on my machine. I killed all the 127 spyware cookies it found, rebooted, and still no joy. So I cleared my yahoo cookies and went to the maps page again - turns out the new maps page requires Flash 9, and if it isn't installed, the only option on the new maps page is to install it or go to the old maps page. Bug in Yahoo's page handler - Flash 9 is not available for Vista 64 or 64-bit browsers, but as soon as the maps page takes you to Adobe to get Flash, it tags your browser as having flash installed, so subsequent visits to the maps site gives you a blank page because no Flash is installed, but Yahoo thinks it is.
So I wiped my yahoo cookies again, and changed my maps link to the old page. Also confirmed Firefox works fine with the new maps page (it's 32-bit). Adobe has no estimate of when Flash 9 will be ready for 64-bit.