I noticed some kind of bug in the scheduler-system of fb. After creating a backup it's not possible to schedule this task in the same step. Under Windows 2008 Server, using the windows task scheduler, it results in an error (StringToOrd in german interface, slightly different in english interface). This is probably caused by the name which fb chooses for new, yet unnamed backups. It contains a blank. After saving the job without a schedule (renaming it to a name without blanks or something) you can edit it and add a job properly.
There's no problem in Windows 7. Just spottet it under 2008 Server.