Consider the following scenario:
You have a Windows 8 or Windows RT PC with multiple user accounts.
An update is downloaded and installed successfully from the Microsoft Store for an installed Microsoft Store app.
A different user logs on to the PC using a different account and attempts to download and install the same Microsoft Store update.
In this scenario, the Microsoft Store update may fail to install.
During the update of an application package, the Custom.Data file is copied from the old package location to the new package location. This works successfully for the first user performing the update. However, when the second user tries to update the same app, the copy from the old package location to the new package location is attempted again but fails because the file already exists. The failed copy results the update not being successfully applied.
Microsoft is aware of the issue and is working on a solution.