Unable to view (access) the checkout

I don't understand why I cannot view checkout page. When I "add to cart", I see this error:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@mywebsite.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

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Maybe I must able some option?
Can I solve?


Here my server log:

[Wed Apr 25 07:17:56 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/404.shtml
[Wed Apr 25 07:17:56 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/favicon.ico
[Wed Apr 25 07:17:56 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/500.shtml, referer: www.mywebsite/it/
[Wed Apr 25 07:13:18 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/404.shtml
[Wed Apr 25 07:13:18 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/favicon.ico
[Wed Apr 25 07:09:21 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/404.shtml
[Wed Apr 25 07:09:21 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/favicon.ico
[Wed Apr 25 07:09:20 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/500.shtml, referer: www.mywebsite.com/it/shop1/product/1.html
[Wed Apr 25 07:03:18 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/404.shtml
[Wed Apr 25 07:03:18 2012] [error] [client 82.50.80.243] File does not exist: /home/brand/public_html/favicon.ico

This page seems inexistent (checkout page)

www.mywebsite.com/it/shop1/checkout.html

What's the problem??

Hi,

Change the code:
if(!isset($this->currentShipping))$this->currentShipping = '';
if(method_exists($this->currentShipping, 'getShippingAddress')) {

to:
if(!empty($this->currentShipping) && method_exists($this->currentShipping, 'getShippingAddress')) {

in the file "address" of the view "checkout" of your front end template via the menu Display->Views and that should solve the problem.