输入字符串的格式不正确c＃

Question

我需要帮助，我收到错误：输入字符串的格式不正确。提前谢谢。

错误选择的行是第一行

var getus = await _instaApi.GetUserAsync(listBox1.Items[s].ToString());
                           var userid = getus.Value.Pk;
                            var FollowResult = await _instaApi.FollowUserAsync(long.Parse(userid));
                            if (checkBox3.Checked == true)
                            {
                                var userFeed = await _instaApi.GetUserMediaAsync(listBox1.Items[s].ToString(), 1);
                                if (userFeed.Succeeded)
                                {
                                    foreach (var media in userFeed.Value.Take(1))
                                    {
                                        var likeResult = await _instaApi.LikeMediaAsync(media.InstaIdentifier);
                                        var postResult = await _instaApi.CommentMediaAsync(media.InstaIdentifier, textBox1.Text);

                                    }

                                }
                            }

字符串值的示例是“username”。