When you upgrade an enrolled Windows RT-based device to Windows 8.1 RT General Availability, all modern apps that were installed through the Company Portal app before the upgrade may not function immediately, and an "X" may be displayed on the apps tile.
This occurs because even though you can open the Company Portal app, you cannot use the apps that were installed from the Company Portal app until the device is connected to the Windows Intune service. After the device is connected, the Windows "side-loading" keys are re-provisioned and the functionality of the apps is restored.
For all the details for this issue as well as a resolution, please see the following:
J.C. Hornbeck | Solution Asset PM | Microsoft GBS Management and Security Division
System Center All Up: http://blogs.technet.com/b/systemcenter/
System Center – Configuration Manager Support Team blog: http://blogs.technet.com/configurationmgr/
System Center – Data Protection Manager Team blog: http://blogs.technet.com/dpm/
System Center – Orchestrator Support Team blog: http://blogs.technet.com/b/orchestrator/
System Center – Operations Manager Team blog: http://blogs.technet.com/momteam/
System Center – Service Manager Team blog: http://blogs.technet.com/b/servicemanager
System Center – Virtual Machine Manager Team blog: http://blogs.technet.com/scvmm
The Forefront Endpoint Protection blog : http://blogs.technet.com/b/clientsecurity/
The Forefront Identity Manager blog : http://blogs.msdn.com/b/ms-identity-support/
The Forefront TMG blog: http://blogs.technet.com/b/isablog/
The Forefront UAG blog: http://blogs.technet.com/b/edgeaccessblog/