Problem

register_globals directive is turned ON in PHP

Solution

Instant Update won't work with register_globals turned ON. Luckily, from PHP6 register_globals directive will be removed and default behavior will be as when this directive is turned OFF

If your server is installed as server module, and not as CGI module you could try to create blank text file, name it .htaccess and place it in your website root folder, and place following lines in it. If such file already exists, just append following code at the end of it:

php_flag register_globals off

Otherwise, if PHP is installed as CGI module create blank text file, name it php.ini and place it in your website root folder, and place following lines in it. If such file already exists, just append following code at the end of it:

[PHP]
register_globals = Off