Lukas, < How does the body of this response look like? Is there some No the browser display a generic error. I do some test but i found different conclusion. In the test i display the same web page, based on some description. I press the submit button when some description addCondition: are false. And when pres / represe the submit button ( with no change on input data ) the answer change( sometime ok , somtime with error ) I have Squeak image " the server " on a notebook. A) When i do web request from the notebook ( Internet Explorer 6.0 ) rarely i have error : HTTP-500. B) When i do request from an another PC in a local network with Windows XP and Internet Explorer 7.0 frequently i have error. The browser display a page with generic error : " Internet Explorer: impossibile visualizzare la pagina -> i can't dispaly the page" C) When i do request from anotehr PC in a local network with Ubuntu and Firefox 3.0.8 sometimes i found the error: " Connection Interrupped The connection to the server was reset while the page was loading. The network link was interruped while negotiating a connection. please try again. " I hope you understand my indication. Dario