I installed "All in One SEO Pack" plugin on Japanese environment.
This plugin contains all_in_one_seo_pack-ja.mo file,
but this plugin is not displayed in Japanese.
So I tried to run msgunfmt.exe command, and it says as follows.
msgunfmt.exe all_in_one_seo_pack-ja.mo -o all_in_one_seo_pack-ja.po
msgunfmt.exe: file "all_in_one_seo_pack-ja.mo" contains a not NUL terminated string
I found that Changeset 50556 causes this problem.
Therefore all_in_one_seo_pack-ja.mo file is corrupted since version 220.127.116.11 (3 years ago!).
If you have PO file, you should re-generate MO file from PO file.