Symptom: When sending a PDF for download to IE, the error message appears:
There was an error opening this document. The file could not be found.
Cache-Control has been set to no-cache. Firefox works fine.
Cause: Unknown, IE specific problem with cache handling.
Solution: Set expiry date to trick browser that content expired. 
response.setHeader("Expires", "0"); response.setHeader("Pragma", "cache"); response.setHeader("Cache-Control", "private");