通过 Web 服务返回大大小字符串时出现 IIS 错误

我想通过网络服务返回图像，所以我尝试将数据库中的图像转换为字节，然后从字节转换为 base64 字符串并将其返回到网络服务，我已经完成了一半，但由于字符串大小或其他方面的限制，我无法返回整个字符串希望？

<%@ WebService Language="C#" Class="Service" %>

using System;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.IO;
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
// [System.Web.Script.Services.ScriptService]
public class Service : System.Web.Services.WebService
{
    public Service () {
        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }
    [WebMethod]
    public string IMAGE(string ID)
    {

        SqlConnection conn = new SqlConnection("Data Source=NEWCRISP19;Initial Catalog=masselango;Persist Security Info=True;User");
        conn.Open();
        SqlDataAdapter sdImageSource = new SqlDataAdapter();
        sdImageSource.SelectCommand = new SqlCommand("select ImageData from ImagesStore where ImageId=('" + ID + "')", conn);
        DataSet dsImage = new DataSet();
        sdImageSource.Fill(dsImage);
        byte[] blob = (byte[])dsImage.Tables[0].Rows[0][0];
        String c = Convert.ToBase64String(blob);
        //c = c.Replace(" ", "");
        return c;

    }
}

web.config 未修改。

帮我检索整个base64字符串。