If the Windows 8.1 tablet is enrolled, the user is unable to use Content Locker.
If a device is not enrolled, the user can download and install the current version of Content Locker (Version 1.7.50). Upon launching Content Locker, you will be asked to put in your server details and credentials, and you will successfully log in and use Content Locker.
This affects WinRT v1.7.
This issue has been given identifier WSCL-173768. This issue has been resolved in Windows 8.1 Content Locker v1.7.66.