Cookie problem

Hi,

I have just upgraded to Vista Ultimate with IE7. For diagnostic purposes
have IE7 set to warn of cookies.

I run a small community website, and I have developed a cookie problem
on-line - my member registration "remember me "
cookie is not getting set, although I am warned that one is about to be set.
Also, cannot reset the cookie with new expiry date.

Off line I have IIS7 installed and there is no problem when running my site
offline - the cookie gets set
and amended as necessary with the same security settings as online. Also, on
another machine running XP Pro with IE6 works fine online.

My webhost is running IIS5. Is there possibly a problem with the
"IIS5/IE7/vistaUltimate" combination???

I'm baffled by this. Any ideas anyone.

Thanks

Hugh