Security is essential. The more sophisticated now days’ attacks the more poking around is needed preventing risks. Microsoft’s secure by design and secure by default paradigm comes however of some additional costs. The remediation expenses are sometimes higher than needed, due to completely misleading warnings or error messages.
Let say you publish an Excel workbook into SharePoint 2010 Excel Services and next you will try to open in Excel client that very same workbook clicking on “Open in Excel” (Picture 1). The next moment you could be confronted with a puzzling error message stating “The file is corrupt and cannot be opened” (Picture 2). It is truly funny afterwards to see the “Was this information helpful?” link as well. Unfortunately the answer is thanks, not at all. As you can assume, the remedy is security related and could be done very easily.
In order to relax the by default set security settings, open Excel and in the backstage view click Options >> Trust Center >> Trust Center Settings… >> Protected View (Picture 3) and uncheck the Check boxes, click OK, OK. Close Excel and try opening your Excel Workbook again (Picture 1). This time the attempt will succeed.