[eluser]jalalski[/eluser]
View the source of the page and make sure that it is correct.
Try saving the HTML of the page locally and then POSTing it.
Check whether mod_security is installed on the server and possibly blocking some things.
When you say "don't post any data" do you mean that the POST array is empty?
Or the form just sits there and doesn't do anything?
More info needed...