Downloading image from URLs

Hi,
im using This Solution to download and save image from url. This Recipe works fine, but when i pass url from a list(iterating using foreach loop ), this code give NullReference Exception, Because ** e.Result** is coming null, i checked the urls ,all of them have images (each image has its own url). I also try to replace webClient.DownloadDataAsync(url); with var bytes=webClient.DownloadData(url);, in this case, application either get crash or hang.

Please suggest if there is any soln to resolve this. Is there any other way to download and save images from URLs without effecting UI .