A: Chances are that the computer is asleep. If the computer is in sleep or hibernation mode, all processes and programs are sleeping as well and the program won't work.
Q- But I have checked Options - Engine -Prevent sleeping!
A- This prevents that the computer falls asleep while the task is being executed. But f the computer is already asleep the task won't even start
Q- Is there any way to wake the computer up before the task starts?
A- If your BIOS supports it, you could program a timer in Windows Task Manager (taskschd.msc ) to wake the computer up before the task starts. This is outside the program's functionality so don't ask me how to do that
Q- Anything else I could do?
A- Set the timer to a time when you surely know that the computer is awake. You could also check the option to "Run missed backups" to start the task when the computer is available.