One of our users was having trouble opening an e-mail attachment that was sent from one of our software applications.  It looked like some kind of permission problem.  When he tried to preview it, it would just say the file cannot be previewed because of an error in the PDF Preview Handler.  If he tried to open it, it would say that it could not save the attachment.  He was previously able to open them without receiving the error.  I found that when you open Outlook attachments, it usually saves them in a randomly named folder under this path:

%userprofile%\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Outlook

This location can be changed with a registry edit.  Since that Temporary Internet Files folder is a special folder, you cannot drill down to this; you must paste or type it into explorer (or your favorite command prompt).

I'm sure you've seen how Windows will create a file with a number in parentheses if a file by that name already exists?  The problem in Grant’s case is that the attachments being e-mailed to him were all named Attachment.pdf, so they were being named Attachment.pdf(1), Attachment.pdf(2), etc.  It seems like the limit was 199 of these renamed files on Grant’s machine.  I have not been able to determine how this limit is determined, and it does not seem to be the same everywhere.  Cleaning out that folder solved his issue (at least until he gets the 200th e-mail again).