LATE BREAKING NEWS: This appears to be an Office 2010 beta issue. Rumor has it (I will confirm later) that VSTO will be installed along with an Excel 2010-only install when Office ships next year. But it does impact us today. Sorry. The latest, late breaking news is that VSTO will continue to be installed with “Office Shared Tools”. You must select it along with Excel 2010 when you install. We have modified the PowerPivot for Excel installation to verify this, but you must still do it. Sorry to raise your hopes. 
A recent issue has come up that us geeks might find interesting. To minimize their expose to Office 2010, some folks are installing just the Excel 2010 app itself. On the surface that sounds like a good idea – only install what you need and don’t add bloatware if it isn’t needed (isn’t that the definition of bloatware? 
http://en.wikipedia.org/wiki/Bloatware ).
The problem is that the PowerPivot Excel add in is written mainly in managed code. And the way managed code interfaces with Excel is through, you guessed it, VSTO (http://en.wikipedia.org/wiki/Visual_Studio_Tools_for_Office). Unfortunately VSTO is only installed if you select the “Office Shared Tools” option as part of your installation, or if you did a “Complete” installation like I always do. See this posting from Ron Pihlgren (a Test lead here in PowerPivot-land) http://blogs.msdn.com/ronpih/archive/2009/11/18/office-14-beta-2-powerpivot-for-excel-ctp3-you-must-install-office-shared-tools.aspx for more info.
Hi,
))
it’s the run time, not VSTO, don’t say things like that!!!
[...] 1) Ensure when you install Excel 2010 that you also install Office Shared Tools, it contains VSTO which is necessary for the PowerPivot add-in to work properly. You can read more in his posting: And oh, you need this one more thing. [...]