Task Scheduler Won't Run WBADMIN Backup

Question

After several weeks of trying, the backup (wbadmin) doesn't work from the task scheduler.  When I enter the WBADMIN Start Backup command directly into a command prompt, it executes perfectly and backs up everything it's supposed to, but for some reason,
when that EXACT SAME COMMAND is executed from the task scheduler it starts, then immediately stops.  I opened the Task Scheduler, clicked on "Task Scheduler Library" in the left pane, and looked at the backup job in the top window of the center pane. 
The "Last Run Result" column simply showed, "(0xFFFFFFFF")".  I also clicked on the job's History Tab, which showed 7 entries at the date/time the job is set to trigger, which indicated that the task started and completed, "successfully" within the same
second (i.e. 01:00:00), but absolutiely nothing is backed up, nor are there any entries for the trigger date on the backup drive.
This has happened four Sundays in a row, and each time, when I subsequently execute the WBADMIN command from a command prompt, it works correctly.  Any ideas about what I'm missing and/or doing incorrectly
Creacon

Answer 1

Thanks Jeff, but unfortunately, I've already done all those things from advice in a previous thread.  The task scheduler DOES schedule the task, and my History is not disabled. But when the Task Scheduler starts, it then stops immediately with two
log entries: 1) "Action Completed", and in the lower history window "Task Scheduler successfully completed the task ...", and 2) a log entry saying "Task Completed", and in the lower history window, "Task Scheduler successfully finished...", but NOTHING
is backed up.  I've gone through the task scheduler settings for the task, and everything seems ok, but no dice.  Yet, I can enter the EXACT SAME wbadmin command into a command prompt, and the backup works fine.
Here's the actual "SCHTASKS" command that I entered to schedule the job:
SCHTASKS /Create /SC  WEEKLY /D SUN /TN CTServerWeeklyBackup /RL Highest /ST 01:00 /TR "WBADMIN START BACKUP -backupTarget:f: -allCritical  -include:C:\,D:\CAB\,D:\Downloads\,D:\Extracts\,D:\SSLCert\,D:\Temp\,U:\CAB\,U:\Shares\,U:\Temp\  >
C:\backupLogs.txt"
The above command executed without incident, then I immediately checked the task scheduler, and the task was there, properly scheduled.  When the trigger time/day occurred, the task simply started then immediately stopped, yet when I enter just
the WBADMIN command into a command prompt, it executes correctly, completely and without incident.
Creacon