title: IIS deletes System.Web.Extensions.dll, why?
body: <p>I moved a site to another server, it worked fine for a a while, but then crashed. I figured out that System.Web.Extensions.dll was missing, so I copied it again. After a while it was missing again.
  Using Process Monitor I figured out that IIS (w3wp.exe) deletes the file soon after I copy it to the bin folder. (CreateFile with "Read Attributes, Delete" access.)</p>
  
  <p>What could cause this behaviour?</p>