I made a post on the WordPress support thread with my fix, though thought I should expand here. This may not fix the issue for all users, as the reloading might be the result of other problems or faulty plugins.

1. Remove any additional rewrite rules from your .htaccess, besides the WordPress-generated code. Remember to back it up!

(If your WordPress settings state that your install is on http://mysite.com, but you are running a .htaccess rule to rewrite http://mysite.com to http://www.mysite.com, you’re running the wp-admin page in a loop of redirects).

2. If you can now log in, go to Settings and change the location of WP and your blog to http://www.mysite.com (assuming this is where you wanted WordPress installed). If your blog or WordPress installation is located in another dirctory or subdomain, don’t change these just add the www.

3. Re-add the .htaccess rewrites.

They might like look this –

Options +FollowSymLinks
RewriteEngine on
RewriteCond %{HTTP_HOST} ^mysite.com
RewriteRule (.*) http://www.mysite.com/$1 [R=301,L]
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index\.html\ HTTP/
RewriteRule ^index\.html$ http://www.mysite.com/ [R=301,L]

(This rewrites http:// to http://www as well as removing index.html or index.php from your URLs)

If the above fix doesn’t work, try removing plugins from your server one by one and then try to log in. An outdated plugin that doesn’t work with your current version of WordPress has also been known to cause this problem.