The "Unix-Enabled" checkbox in the "Unix Account" tab of the Management Console for Unix (MCU) is disabled (grayed out) and so the user can not be unix-enabled.
原因
The account that is being used to access the MCU doesn't have the required permissions to modify the account that needs to be Unix-enabled.
解决办法
The permissions in AD need to be corrected so that the account to Unix-enable can be modified.