ASP.NET Excel writing over network fails

I am developing an ASP.NET application ( with VS 2010   f/w   .NET4 . The webserver is Win2008 R2 ENT, 64bit )
The  IIS Website  Application is using Application Pool and the pool has  a dedicated identity user  

There is a component of copying an excel template to a working directory and write  some data on that

 Everything works fine   if I use the local path  ( Like E:\ExcelDirectory)
 
   if I use the the same path but as network path  ( like \\weserver\ExcelDirectory  )   the writing hangs forever
    But if I use my account as apppool user , even on network path everything works fine

    I have given  the write permission to the apppool user ( even the apppool user is added as administrator)

    Essentially, the issue may be  about privileges the apppool user doesn't have and my user has  ( Is there anything like a previlage to write over network ? )