Were any courses backed up manually before the attempt to setup with cron + automatted backups? in a course itself ... backup link in the course admin menu. Think your last post said you tried that and it worked. Hmmmmm ....
This problem started with one setting up cron on a system that doesn't know about 'cron' with:
c:\php\php.exe -f c:\moodle\admin\cron.php > c:\moodle\admin\cron.log
Once setup, the courses weren't being backed up. So have you tried the command above from the command line without the redirect output going to a cron.log file? The batch file setup for that runs as what user?
If one were to just use the browser ... http://yoursite/admin/cron.php what happens? Run that way, cron.php execution is by the web server user, is it not? (same as being logged on as a teacher and teacher clicking the backup link in course menu).
On this page:
http://docs.moodle.org/23/en/Cron_with_Windows_OS
it does show some alternatives. Can only suggest one tries something new if what's there isn't working!
'spirit of sharing', Ken