Internet Security, etc., can also prevent logins if the security is set to maximum levels.
If that does not work... keep reading....
Sometimes enabling cookies is not enough. This problem is most common on Windows XP Home using Internet Explorer (IE) 6.0 128-bit.
Microsoft's recent IE updates have put an unnecessary strangle on many normal, safe Internet uses. It unnecessarily restricts what it calls "third-party cookies".
To fix this in Internet Explorer:
Goto TOOLS -> INTERNET OPTIONS -> PRIVACY tab ->
then PUT SETTINGS to "LOW" ...
I use Windows ME with IE 5.5 and Windows XP Pro with IE 6.0 using Norton
Internet Security and have zero problems logging in. I use the "custom" settings to allow third-party cookies on my system.
Do not let terms like "security" and "privacy" disturb you. What normal people consider "security" and "privacy" is different than the techie uses of those words. You are in no danger visiting this site, which is hosted on a reliable server in the United States.
Even banks and other companies suffer from this inadequacy of the Microsoft software. It's sad how these updates can prevent us from doing normal work, yet cannot seem to keep out the real problems: spam and new virus attacks.
A common misconception is that "cookies are bad" .. when in fact, cookies are the little pieces of code that keep you logged into a system like this one. It's temporary website memory to make your trip easier. It's what allows you the option to always visit a site and keeps you logged in even after the computer has been reset.