I changed my computer name a while ago.
Today, when I went to the Task Scheduler to add a new task, I got an error message:
"An error has occurred for task [task name ]. Error message: The specified account name is not valid."
When I clicked on OK to clear the error the Task Scheduler opened okay, but the task identified in the error did not appear in the list of tasks, meaning that it was impossible to examine the task or correct the error.
When I checked the file containing the task details I found that the task still had the old computer name, i.e. it had not been updated when I changed the computer name, and so the task was now causing an error, and apparently, was being hidden.
This would seem to be a bug. Preferably, the account names should be updated if the computer name is changed, or at least the task should still be visible in the Task Scheduler.