If a Restricted Finder Setup does not allow the user to have access to the Control Panels, PC Exchange does not work, and the Macintosh treats the disk as a non-Macintosh formatted disk.
You can work around this by adding the PC Exchange Control Panel to the Restricted Finder Items folder. This gives the setup access to only that particular control panel. Once this control panel is put in the "Items for this Setup", PC disks mount without a problem.