Adding www makes everything stop working
 

We switched to a dedicated server and since then I have noticed a weird issue. If you goto mydomain.com everything loads fine. However if you goto www.mydomain.com it logs you out and some things do not load. If you go back too mydomain.com everything is fine again and you are logged in. I can not figure this out at all.

Path to Save Cookies is "/"

Cookie Domain is (blank)

Nothing appears in the drop down boxes

What do you have in your Site Name / URL / Contact Details and do you have a htaccess file in your ftp

Ask your host to do a redirect from www.site.com to just site.com .

Or, change your cookie domain (AdminCP > Settings > Options > Cookies and HTTP Header Options > Cookie Domain) to ".yoursite.com" (no quotes, but note the period at the beginning). You will probably need to clear your browser cookies after making this change.

Just add the following to your .htaccess file and you should be good to go:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www.yourdomain.com [NC]
RewriteRule ^(.*)$ http://yourdomain.com/$1 [L,R=301]

This could be due to a few things.

This might not even be a server-sided issue, it could be a Domain DNS issue. It could also be an .htaccess/web.config issue. If it is a server-sided problem, check your Domain DNS on your server.