You may receive the following message while opening a specific schedule task or running it manually from Windows Task Scheduler:
The selected task “{0}” no longer exists. To see the current tasks, click Refresh.
While you are receiving this error in GUI, it is possible that your tasks are still running but you are just unable to manage them from GUI. There are multiple solutions and causes for this issue but the below is the simple solution to resolve this:
[1] Go to “%windir%System32LogFiles” directory.
[2] If Scm folder does not exist, create Scm folder.
[3] Reboot your system/server and then try to edit your tasks.
If this steps do not resolve the issue, you will need to check this further to find out other root cause.