What happens if you try to schedule another job for one of the customers that have already been successfully scheduled? Is the problem limited to just certain customers? Of the customers that aren't showing up, are they assigned to the same route (on the Route screen) as some of the customers who do show up on the calendar?
If you would like us to analyze your database to see what's causing the problem then you can send us a backup file via email. To do that go to File | Backup, set the backup name to C:\GOPHERBACKUP.ZIP, click Backup and then email the C:\GOPHERBACKUP.ZIP file to firstname.lastname@example.org.