Checkout - page not found

I don`t know what's happening. When I proceed to check out appear this error

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I don`t know why apparently everything is ok.

Does someone can help me?

Thanks.

P.S This error occurs when I try access the shipping address also.

Could you check whether the same happen on default Joomla! template like Beez ? You can also disable SEF URL's if they are enabled to make sure that it is not something related with your hosting.

I already done and still the problem. what can I do more?
I`m almost done with this project and I don`t what can I do.

Thanks

If the problem is also on default J! template the only way is to update VirtueMart or reinstall it. VirtueMart as a 3rd party extension is beyond our support. For more help please contact with extension support forum.