PI system backup

I am trying to do a backup of historical data onto my external usb drive. I have created a bat file with the parameter

pibackup e:\daily historical data 100

I have placed this bat file in C:\Program Files\Rockwell Software\FactoryTalk Historian\Server\PI\adm>

Then using windows scheduler i try to run it everday at 10 at night. What i have noticed is when i manually open a command prompt and run this command the files are successfully backed up. But when i use it in windows scheduler this doesnt work.

Any suggestion to make this work would be helpful.