v1.31 EPUB>EZW conversion suddenly fails

[elipsett]

I've been using Calibre quite happily for some time, and a few days ago used it to convert a number of epub files into AZW format for Kindle. They all converted painlessly (and automatically), downloaded to the Kindle, and read fine.
Earlier I tried to do it again, and this time the conversion failed with an error message (below).
I tried the conversion on multiple files, including one that I successfully converted a few days ago. I reinstalled Calibre. I installed an older version of Calibre. I did a few other things. The result is the same... identical error message and no output.

I haven't made any changes to my system recently, but of course there are automatic upgrades to Windows7 and security software.
My system is running the native Japanese OS, in Japanese language mode, but until now this has never caused any sort of problem.
The books being converted are English-language books created in the US.

Any suggestions would be welcome.
Thank you.

Edward Lipsett


===========================
calibre, version 1.31.0
ERROR: Unhandled exception: <b>error</b>123, 'CreateFile', '?????????????????????? ???????????????')

calibre 1.31 isfrozen: True is64bit: False
Windows-7-6.1.7601-SP1 Windows ('32bit', 'WindowsPE')
('Windows', '7', '6.1.7601')
Python 2.7.5
Windows: ('7', '6.1.7601', 'SP1', 'Multiprocessor Free')
Traceback (most recent call last):
File "site-packages\calibre\gui2\convert\single.py", line 272, in accept
File "site-packages\calibre\gui2\convert\metadata.py", line 236, in commit
File "site-packages\calibre\db\legacy.py", line 465, in set_metadata
File "site-packages\calibre\db\cache.py", line 57, in call_func_with_lock
File "site-packages\calibre\db\cache.py", line 1150, in set_metadata
File "site-packages\calibre\db\cache.py", line 1145, in set_field
File "site-packages\calibre\db\cache.py", line 946, in set_field
File "site-packages\calibre\db\backend.py", line 1392, in windows_check_if_files_in_use
File "site-packages\calibre\utils\filenames.py", line 348, in __init__
error: (123, 'CreateFile', '?????????????????????? ???????????????')

[elipsett]

A lot more work on deleting and re-installing Calibre. No change.

The problem is not limited to epub>AZW conversions, however... the same error message is returned for ALL conversions.

[BetterRed]

@elipsett - Try giving calibre a dedicated location for its temporary files - via the CALIBRE_TEMP_DIR Environment variable - see http://manual.calibre-ebook.com/cust...ment-variables

BR

[elipsett]

After considerable research and a fair amount of trial-and-error, I discovered that the system locale setting for non-Unicode programs (region & language, in the control panel) had been set to English, whereas this machine is a Japanese-native system. I reset it to run Unicode programs as Japan, and the problem is all gone.
Hopefully this explanation will help somebody else solve this problem someday!