A role-based user having access to Group Management role will not be able to access Rights to Files and Folders under Modify Group by default until the File System Rights page is assigned to them.
To assign File System Rights page for RBS users:
Log on to iManager with administrative credentials.
Click Configure > Role Based Services > RBS Configuration.
The list of collections for the RBS setup is displayed.
Click an RBS setup collection > Property Book tab and then select Modify Group.
From the Actions menu, click Page List and the Edit Page List is displayed.
Select File System Rights page from the Available Pages list, add it to the Assigned Pages, then click OK.
The Files System Rights page is assigned to RBS Users.