与 localhost 的连接已中断。这个问题

 为什么点一下上传按钮就会出现什么与 localhost 的连接已中断。
asp：</head>
<body>
    <form id="form1" runat="server">
    <telerik:RadStyleSheetManager ID="RadStyleSheetManager1" runat="server">
    </telerik:RadStyleSheetManager>
    <telerik:RadScriptManager ID="RadScriptManager1" runat="server">
    </telerik:RadScriptManager>
    <div>
    <asp:FileUpload ID="fulDoc" runat="server" Width="230px" />
                    <telerik:RadButton ID="btnPPDocumentUpload" runat="server" Text="上传" 
                        Width="80px" onclick="btnPPDocumentUpload_Click"></telerik:RadButton>
    </div>
    </form>
</body>
</html>C#:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;namespace ZLSP1017.MaterialManagement
{
    public partial class MmUpLoad : System.Web.UI.Page
    {
        ZLSPBLL.BLL.ZL_Document bllDocument = new ZLSPBLL.BLL.ZL_Document();
        ZLSPBLL.BLL.ZL_DocumentType bllDocumentType = new ZLSPBLL.BLL.ZL_DocumentType();
        ZLSPBLL.Model.ZL_Document modelDocument = new ZLSPBLL.Model.ZL_Document();
        ZLSPBLL.Model.ZL_DocumentType modelDocumentType = new ZLSPBLL.Model.ZL_DocumentType();
        protected void Page_Load(object sender, EventArgs e)
        {        }        protected void btnPPDocumentUpload_Click(object sender, EventArgs e)
        {
            if (fulDoc.HasFile)
            {
                bool HasType = false;
                bool HasSize = false;
                string typeId = "";
                string fileType = System.IO.Path.GetExtension(fulDoc.FileName).ToString().ToLower();
                DataTable fileTypeList = bllDocumentType.GetList(" DTExtension = '" + fileType + "' ").Tables[0];
                if (fileTypeList.Rows.Count > 0)
                {
                    HasType = true;
                    if (fulDoc.PostedFile.ContentLength / 1024 <= int.Parse(fileTypeList.Rows[0]["DTCapacity"].ToString()))
                    {
                        HasSize = true;
                        typeId = fileTypeList.Rows[0]["DTId"].ToString();
                    }
                }
                if (false == HasType)
                {
                    Response.Write("<script>alert('不合法的文件类型！');</script>");//不合法的文件类型
                    return;
                }
                if (false == HasSize)
                {
                    Response.Write("<script>alert('文件大小超出范围！');</script>");//文件大小超出范围
                    return;
                }
                string saveName = System.IO.Path.GetFileNameWithoutExtension(fulDoc.FileName.ToString());
                string fileName = DateTime.Now.ToString("yyyyMMddHHmmss") + fileType;
                string filePath = "../UploadFiles/ProfessionProject/" + System.DateTime.Now.ToString("yyyyMM") + "/" + fileName;
                bool hasDirectory = System.IO.Directory.Exists(Server.MapPath("../UploadFiles/ProfessionProject/" + System.DateTime.Now.ToString("yyyyMM") + "/"));
                if (hasDirectory)
                {
                    fulDoc.SaveAs(Server.MapPath(filePath));
                }
                else
                {
                    System.IO.Directory.CreateDirectory(Server.MapPath("../UploadFiles/ProfessionProject/" + System.DateTime.Now.ToString("yyyyMM") + "/"));
                    fulDoc.SaveAs(Server.MapPath(filePath));
                }
                modelDocument.MIId = bllDocument.CreateId();
                modelDocument.DTId = typeId;
                modelDocument.MIName = saveName;
                modelDocument.MIPath = filePath;
                bllDocument.Add(modelDocument);                //文件上传完成
                Response.Write("<script>alert('文件上传完成！');</script>");//文件上传完成
            }
            else
            {
                Response.Write("<script>alert('请先选择文件！');</script>");//请先选择文件
                return;
            }
        }
    }
}