I'm having this problem as well.
My server config:
X-Cart Gold 3.5.7, original source
Smarty 2.5.0
PHP 4.3.6
MySQL server 4.0.16-standard
MySQL client 3.23.49
Web server Microsoft-IIS/5.0
The Javascript error:
Line: 40
Char: 2
Error: 'parentNode' is null or not an object
Code: 0
URL:
http://mysite/customer/home.php