Hi, 
When I try to open PowerPivot 
I'm getting following error:

file:///C:/Program Files (x86)/Microsoft Analysis Services/AS Excel Client/10/Microsoft.AnalysisServices.Modeler.FieldList.vsto

Downloading file:///C:/Program Files (x86)/Microsoft Analysis Services/AS Excel Client/10/Microsoft.AnalysisServices.Modeler.FieldList.vsto did not succeed.

I cannot see PowerPivot tab in excel and this addin is enabled in COM addins. 
 Please advise.

Hi John,

Could you tell me which version of Office are you using?

For your issue please refer to this blog, you need to run Office Setup / Add or Remove Features, then check .NET Programmability Support under Microsoft Excel.

http://blogs.msdn.com/b/michen/archive/2011/01/28/undocumented-powerpivot-installation-requirement.aspx

You can also refer to this discussion about your issue:

https://social.msdn.microsoft.com/Forums/sqlserver/en-US/572168c3-7faf-41a6-88b4-790a9cd223d0/install-issues-for-powerpivot-for-excel-read-this

You can get more information about your issue.

If you need more help with Power Pivot please post your issue in Power Pivot forum:

https://social.technet.microsoft.com/Forums/office/en-US/home?forum=sqlkjpowerpivotforexcel&filter=alltypes&sort=lastpostdesc

The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.

Hope its helpful.

Regards,

George Zhao
TechNet Community Support