I've got a favor to ask of anyone who's got the FM version of PHP installed on Windows, FMS 12 &/or 13.
Can you tell me if PHP's "mbstring" extension is enabled?
(put a page on your server that contains only:
<?php phpinfo(); ?>
then load that page in a browser and do a search for "mbstring")
For security, you should not leave this page on your server
In my experience, mbstring is enabled in the Mac version of FM's PHP (both 12 & 13) but is not enabled in the Windows version (12). Unfortunately, I've only got one Windows machine I can check, hence this appeal ;-)
FWIW: mbstring is a handy extension used by things like mPDF, mb_strtoupper(), etc.