Uploading files whose size> 1MB and save to a folder

I am trying to upload files to a folder on my harddisk whose size is greater than 500kb but i always get the message Http Error 400 BAD REQUEST . IIS is not installed on my profile so i didnt add <system.webserver> settings to the web.config file ('m using ASP.Net Development server i.e inbuilt)
As per my knowledge i had made changes to the web.config file as below

<configuration>
	<connectionStrings>	
    <add name="connection" connectionString="server=PRATHAPG\SQLEXPRESS;database=Prathap;trusted_connection=true"/>
	</connectionStrings>
	<system.web>
    
		<compilation debug="true" targetFramework="4.0"/>
    <httpRuntime maxRequestLength="204800" executionTimeout="3600" maxQueryStringLength="1024000"/>
	</system.web>    
    
  </configuration>

The code for uploading the files

SqlConnection Cn;
    SqlCommand Cmd;
    SqlDataAdapter Da;
    DataSet Ds;

    protected void Page_Load(object sender, EventArgs e)
    {
        string conn = ConfigurationManager.ConnectionStrings["connection"].ConnectionString;
        Cn = new SqlConnection(conn);
        Ds = new DataSet();
        Cmd = new SqlCommand();
        Cmd.Connection = Cn;
        
    }
    protected void btnupload_Click(object sender, EventArgs e)
    {
        if (ful.HasFile)
        {
            string path = "~/Docs/" + ful.FileName;
            string filename = Path.GetFileName(ful.PostedFile.FileName);
            string fileExtension = Path.GetExtension(ful.PostedFile.FileName.ToLower());
            if (fileExtension == ".pdf" || fileExtension == ".txt" || fileExtension == ".docx" || fileExtension == ".doc" || fileExtension == ".xls" || fileExtension == ".xlsx" || fileExtension == ".ppt" || fileExtension == ".pptx")
            {
                string documentType = string.Empty;
                switch (fileExtension)
                {
                    case ".pdf":
                        documentType = "application/pdf";
                        break;
                }

                ful.SaveAs(Server.MapPath(path));
                Cmd.CommandText = "Files_Insert";
                Cmd.CommandType = CommandType.StoredProcedure;
                Cmd.Parameters.AddWithValue("@Filename", filename);
                Cmd.Parameters.AddWithValue("@Contenttype", documentType);
                Cmd.Parameters.AddWithValue("@Fileurl", path);
                Cn.Open();
                Cmd.ExecuteNonQuery();
                Cn.Close();
                lblmsg.Text = "Uploaded Successfully";
            }
            else
                lblmsg.Text = "Only Pdf,Word,Excel,Text files can be Uploaded";         

Can you please suggest any other alternative and let me know the reason y i am not able to upload files whose size > 500KB even when i added necessary settings in web.config file.