For the past several months I have worked on an issue with the Excel Interactive Preview throwing the error:
"Server Error
404 – File or directory not found.
The resource you are looking for might have been removed,
had its name changed, or is temporarily unavailable."
When refining a SharePoint Search:
We have determined the root cause and this will be fixed in the SharePoint 2013 May Public Release.
SharePoint patching demystified
http://blogs.technet.com/b/stefan_gossner/archive/2014/08/19/sharepoint-patching-demystified.aspx