The update changed some things on the site, therefore some cookies, which safe the login data (such as username and password), are not working properly.
To solve this problem, click on this link:ucp.php?mode=delete_cookies
This will delete your kiteforum.com cookies and next time you login click to save your your username and password again, then it should work.
Every time you should have this problem again, do this again.
The link can also be found on the index site http://www.kiteforum.com
below the last forum listed:
"Delete all board cookies"
If this does not help, then delete all cookies manually.
Delete all from http://www.kiteforum.com
Find a how to guide here:http://www.aboutcookies.org/Default.aspx?page=2
I hope this will help! If not, mail me: info@kiteforum.....