add to cart does not work

sometimes add to cart does not work and the browser is t elling me that is transfering data from www.chaosserver.com
sometimes is working, but it can be like this...
what should i do?

What additional extensions you installed? We are not anyhow affiliated with chaossoftware.com. Please give me your link to check this.

when i am accesing the site by adress http://domain it does not working...
but when i use www.domain it's working.

First of all, such configuration of site is not good for SEO. You should redirect non-www version to www version or vice versa. Use this lines in your .htaccess file
In above case, in VM configuration > Security, you should enter link with www.