Troubleshoot a PowerPivot for SharePoint Installation
If you get errors instead of the pages and features you expect, do the following.
Review release notes for both SharePoint and SQL Server 2014 to get workarounds for known installation problems. Release notes are provided with the installation media or on the Microsoft site from which you downloaded the software.
See the Technet wiki topic, Troubleshooting Installations of PowerPivot (and other add-ins).
PowerPivot Gallery Thumbnail images show as a red X
One Possible cause is the PowerPivot features Integration for Site Collections is not active. Complete the following:
In the PowerPivot Gallery library, click Site Settings from either the gear icon or the Home list.
In the Site Collection Administration section, click Site Collection Features.
Click Site Collection Features.
Verify PowerPivot features Integration for Site Collections is Active.
For additional causes of this issue, see PowerPivot Gallery shows Red X's for Icons (http://support.microsoft.com/kb/2361559).