When we create an asp.net application it manages to write to the filesystem if its on a development server. How ever after hosting on the IIS it might cause problems

For this we use windows impersonation 

try
  {

  WindowsImpersonationContext wic = null;//initialize
  IPrincipal p = this.User;//principal for the authentication
  WindowsIdentity wi = (WindowsIdentity)p.Identity;//casting is neccesary
  wic = wi.Impersonate();
  }
  catch(Exception ie)
  {
  Response.Write("Can Not Impersonate : "+ie.Message);
  }