Task Scheduler not running batch file as expected

[convertingjam]

I have written a simple batch file using XCOPY to copy new or changed files to a separate drive. It works perfectly when run manually. However, after setting it up in Task Scheduler to run every evening, it supposedly completes successfully, but no files are copied.

I've tried changing user groups, setting it to run even if not logged on, defining it to run with the highest privileges, and running it as an administrator.

I'm out of ideas. Has anyone else encountered this issue? How can I fix it?

Thanks.