Issue: A client was experiencing very strange behavior following an upgrade from MOSS 2007 to SharePoint 2010 Server. In a nutshell some documents such as Word (.doc and .docx) would open while others such as Excel (.xls and xlsx) and PDF documents would not open. Note: By open I mean when clicking on an Excel document, stored within a document library, it would not open in Excel installed on Windows 7, Vista, XP, etc. Furthermore, the file type icons that normally display next to familiar documents such as Excel were missing and a missing image red x...