If you have Windows 8 and have created a Windows to go USB drive, one of the restrictions that is applied to Windows To Go machines is that the Windows Store is disabled by default. If you are in a domain environment, you might have enabled a policy that doesn't allow the Windows Store to install apps on Windows to go Workspaces.
Go to the group policy editor. You can go to the gpmc.msc for the Active Directory Group Policy Management Console, or gpedit.msc for the local Group Policy Editor.
Go to Computer Configuration/Administrative templates\Windows Components\Store.
Go to the “Allow Store to install apps on Windows To Go workspaces” policy.