I set the proxy page and it works good. I can get access to the desired layer (Map Server) with url: http://[machin.name]/proxy.ashx?[url to layer] in the browser.
But I cannot find any field ProxyUrl for ArcGISDynamicMapServiceLayer class. Using the same url as above causes the error "Bad request" during layer loading.
I was not able to find related information in documentation and forum. So I ask here: is it possible to load secure Dynamic layer using the proxy page?