同样的一段程序，为什么我的本地可以用，上传到服务器就不能用了？
using   System;
using   System.Data;
using   System.Configuration;
using   System.Collections;
using   System.Web;
using   System.Web.Security;
using   System.Web.UI;
using   System.Web.UI.WebControls;
using   System.Web.UI.WebControls.WebParts;
using   System.Web.UI.HtmlControls;
using   System.Drawing;
public   partial   class   FS_OA_webs_UploadPic   :   System.Web.UI.Page
{
        private   int   newwidth;
        private   int   newheight;
        private   System.Drawing.Bitmap   b;
        protected   void   Page_Load(object   sender,   EventArgs   e)
        {
                if   (!Page.IsPostBack)
                {
                        UploadPan.Visible   =   true;
                        UploadedPan.Visible   =   false;
                }
        }
        protected   void   UploadBtn_Click(object   sender,   System.EventArgs   e)
{
if(Page.IsValid)
{
if(UploadFile.PostedFile.ContentLength/1024> 2024)
{
Response.Write( " <script   language= 'javascript '> alert( '上传的图片过大！ '); </script> ");
}
else   if(UploadFile.PostedFile.ContentType.ToLower().ToString().Substring(0,5)!= "image ")
{
Response.Write( " <script   language= 'javascript '> alert( '上传的文件的类型不正确！ '); </script> ");
}
else
{
string   num=UploadFile.PostedFile.FileName;
int   i=num.LastIndexOf( '. ');
string   newtype=num.Substring(i);
string   newname=System.DateTime.Now.Year.ToString().Trim()   +   System.DateTime.Now.Month.ToString().Trim()  
+   System.DateTime.Now.Day.ToString().Trim()   +   System.DateTime.Now.Hour.ToString().Trim()   +   System.DateTime.Now.Minute.ToString().Trim()
+   System.DateTime.Now.Second.ToString().Trim()   +   UploadFile.PostedFile.ContentLength;
b=new   System.Drawing.Bitmap(num);

if(b.Width> 100)
{
newwidth=100;
newheight=(b.Height*newwidth)/b.Width;
System.Drawing.Image   img=b.GetThumbnailImage(newwidth,newheight,null,IntPtr.Zero);
img.Save(Server.MapPath( "images\\SmallImage\\ "+newname+newtype),System.Drawing.Imaging.ImageFormat.Jpeg);

}
else
{
UploadFile.PostedFile.SaveAs(Server.MapPath( "images\\SmallImage\\ "   +   newname   +   newtype));
}
if(b.Width> 600)
{
newwidth=600;
newheight=(b.Height*newwidth)/b.Width;
System.Drawing.Image   img=b.GetThumbnailImage(newwidth,newheight,null,IntPtr.Zero);
                                                img.Save(S