Recently upgraded from 3x to 4.1.3, and users are having troubles logging in.
I've seen the oft quoted:
If you allow users to login to your site via both
http://www.yoursite.com and just yoursite.com., then you MUST have your cookie domain (vboptions > cookies > cookie domain) set to ".yoursite.com" (no quotes, but note the period at the beginning) or your users will have problems. Also, make sure to tell your users to click the Remember Me button when they login.
However, my forums is at
http://forums.mydomain.com and yes, my cookie settings are at ".mydomain.com"
They ARE getting logged in, as if they click anything the next page shows them as logged in. Just the re-directed page isn't showing it.