Just came across a cookie issue on subdomains. Everything works great in Firefox, but sometimes doesn't work in IE.
I set the cookie on example.com (or subdomain.example.com) and the cookie can be read on some subdomains, but not others. I finally detected a pattern: - example.com works - www.example.com works - subdomain.example.com - sub-domain.example.com works - sub_domain.example.com does NOT work
Other than banning IE (heh) or redirecting sub_domain.example.com to sub-domain.example.com (ick- thousands links and indexed pages to the underscored subdomains), any possible fix?
It's important to note that underscores are not permitted in domain names or hostnames. Only A-Z, a-z, 0-9, and the hyphen (-) are allowed in domain names, so it would appear that you have an invalid hostname of "sub_domain".
It's often a "gotcha" for many Windows users. Windows is non-compliant when it comes to this particular RFC(s). Check out the links from the wikipedia article regarding Restrictions on valid host names [en.wikipedia.org]. This old discussion [ops.ietf.org] on the IETF newsgroup may be helpful too.