I've recently ran into this several times, so I'm thought I'd document it here.
I've created batch jobs (.bat) that do various things, like copy, move, delete files, download stuff from SFTP servers, etc. In the past, I've just used my credentials to run these jobs, but if I changed my password, the jobs would fail. Now, our IT department created a service account for me to Schedule these tasks, but I've had many issues with Scheduled Tasks not working once I changed the credentials to the service account.
The scheduled task will not show an error code, it just won't work or it will be stuck in a "running" state.
Here is what I have found out:
1. The service account should be a local admin
2. Delete your old Scheduled Task
3. Log onto the server using the service account credentials
4. Re-Create the Scheduled Task while logged on as the service account and use the service account credentials
This applies to Scheduled Tasks that run a .BAT file. All my other scheduled tasks work normally.