Check your page source to see exactly what the url is that they are having you follow. Compare it to what it should be. What is the difference?
Try disabling your modifications/plugins and see if you still have this problem.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php
PHP Code:
define('DISABLE_HOOKS', true);
Don't forget that for vbseo, disabling the modification means to also get rid of anything extra you added to your htaccess file.