Windows Scheduled Task: What are the minimum user rights needed for the task?

Solution 1:

Other than the filesystem permissions, you'll need to allow Log on as a batch job. It controls allowing the session to be created for a scheduled task.

The task scheduler should put the user in that allow list when you create the task. You can confirm with the Local Security Policy tool. The other possibility is that it's configured through group policy, in which case, do some digging in the resultant set of policy and find the GPO that needs changed.

Here's the other thing: Check out the permissions on c:\windows\system32\cmd.exe. They're funky. If you've removed the user from the Users group, it can't run cmd.exe by default, which tends to be a big part of running a batch file. Add the user to that ACL, with read/execute. Check any and all executables the batch file needs to touch.