Invalid URI: The hostname could not be parsed

I had a space after "http:// " like http:// exampleServer/exampleservice.svc which had caused this error.

Call Uri.TryCreate:

string original = reviews[e.Item.ItemIndex].URL.ToString();
if (!original.StartsWith("http:"))
    original = "http://" + original;
Uri uri;
if (!Uri.TryCreate(original, UriKind.Absolute, out uri)) {
    //Bad bad bad!
}