Occasionally, when an editing session is up for several days, but no feature that creates temporary files has been used, some administrative script (especially on multiuser or server systems configured to run for months at a time) may decide that Vim's temporary file directory is stale, because it hasn't been accessed in N days, and remove it.
Unfortunately, Vim's error reporting when this happens may not identify the missing directory path; for example:
:hardcopy E324: Can't open PostScript output file
Fortunately, it is easy to determine the temporary file directory path:
:echo tempname() /tmp/v012345/67
or even to recreate it, without ever leaving Vim: