I know you got frustrated with this problem, but after knowing the answer you will cetainly laugh :)
To remove this error, you need to comment (add ; before) the extension for domxml in php.ini - or actually BOTH of the php.ini files in XAMPP:
[path to xampp folder]/php/php.ini
and:
[path to xampp folder]/apache/bin/php.ini
;extension=php_domxml.dll
Do not forget to restart your apache, sometimes you need to restart your computer.
Hope this help you to laugh and resolve the error :)
