Why can't a Task Scheduler job access a mapped network drive?

Mapped drives are a User Interface concept and are not available to background tasks like that. Access the target via UNC and make sure that the user that the task runs as has access to the target.

In my case all i had to do was uncheck the run with highest privileges flag but im running the task in on the same user as the user who mapped the drive.

Try using:

pushd \\machine\share

within a batch file of your scheduled task. Network shared drives are only available from a user-run environment. "pushd" will allow it to be run in the context of the script.

When you're done use:

popd \\machine\share

to unmap the drive.

Reference: https://blog.adrianbanks.co.uk/windows/2007/03/08/accessing-network-file-shares-from-a-command-prompt.html