When creating/modifying a schedule in the advanced options, when selecting processes to not run the scheduled task, if you use the ADD button in this window to select a process (i.e. if the process isn't already running so not in the list of running processes) . You can browse to the process desired and select it.
However if you do this the path to the selected process is included with the process name and the resultant task created in Task Scheduler uses this path as the path to DF64.exe, instead of the correct defraggler path - so the task can never run. (using the running process list instead of the add button works fine, it's only when using the add button).