Only Administrator can see the "Windows Previous Versions" from shadow copies

I used the ReadyNAS (version 6.10.3) admin webpage to schedule snapshots for file shares, and there is an option called "Allow access to Windows Previous Versions". It has already linked up the AD, some users or groups have full access rights of the folders and files that is the same as the full rights of the Administrator, but the users and the groups still cannot see the "Windows Previous Versions". 

What is the possible reasons?

Thanks.