Error - An invalid data source is being used for rptData

try this

using Google.Apis.Services;
using Google.Apis.YouTube.v3;
using System;
using System.Collections.Generic;

namespace MyApp
{
    class YouTubeVideos
    {
        public static List GetVideosList()
        {
            List youTubeModels = new List();
            try
            {
                var yt = new YouTubeService(new BaseClientService.Initializer() { ApiKey = "YourAPIKey" });
                var channelsListRequest = yt.Channels.List("contentDetails");
                channelsListRequest.ForUsername = "mipaltan";
                var channelsListResponse = channelsListRequest.Execute();
                int VideoCount = 1;
                foreach (var channel in channelsListResponse.Items)
                {
                    var uploadsListId = channel.ContentDetails.RelatedPlaylists.Uploads;
                    var nextPageToken = "";
                    while (nextPageToken != null)
                    {
                        var playlistItemsListRequest = yt.PlaylistItems.List("snippet");
                        playlistItemsListRequest.PlaylistId = uploadsListId;
                        playlistItemsListRequest.MaxResults = 50;
                        playlistItemsListRequest.PageToken = nextPageToken;
                        var playlistItemsListResponse = playlistItemsListRequest.Execute();
                        foreach (var playlistItem in playlistItemsListResponse.Items)
                        {
                            YouTubeModel youTubeModel = new YouTubeModel();
                            youTubeModel.itemIndex = VideoCount;
                            youTubeModel.videoId = playlistItem.Snippet.ResourceId.VideoId;
                            youTubeModel.title = playlistItem.Snippet.Title;
                            youTubeModels.Add(youTubeModel);
                            VideoCount++;
                        }
                        nextPageToken = playlistItemsListResponse.NextPageToken;
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine("Some exception occured" + e);
            }
            return youTubeModels;
        }
    }

    public class YouTubeModel
    {
        public int itemIndex { get; set; }
        public string videoId { get; set; }
        public string title { get; set; }
    }
}

in your code

var youTubeList = YouTubeVideos.GetVideosList();
if (youTubeList != null)
{
    rptData.DataSource = youTubeList;
    rptData.DataBind();
}