Background Information
When generating an Excel Visual Report in Microsoft Project 2007 with Office 2010 installed, the process fails with an error dialog. The dialog states, "An unkown error has occurred. An error occurred and the requested action could not be completed at this time."
Resolution
Visual Reports in Microsoft Project 2007 do not work with Microsoft Excel 2010 if you did a clean install of Office 2010 and did not upgrade from Office 2007. If you previously had Office 2007 installed on your PC or laptop, and then upgraded to Office 2010, Visual Reports will still work since the shared component on which Visual Reports depend will still be installed.
Visual Reports in Microsoft Project 2007 use OLAP8 which was included with Office 2007 but not included in Office 2010. To work around this problem, you must install Excel 2007 and then run a repair operation on Office 2010 to make it the default version of Office. You do not need to install Visio 2007, however; after you install Excel 2007, Visual Reports will work with Visio Professional 2010.