I'm running Office Professional Plus 2010 on windows 7 64 bit Ultimate . Excel is Version 14.0.4760.1000 The Microsoft.AnalysisServices.Modeler.FieldList.dll version is 10.50.1600.1 PowerPivot for Excel is listed as Com Add-In. When I bring up the "COM Add-Ins" dialog, the PowerPivot for Excel Add-In is listed but unchecked. Load Behavior is "Load at Startup". If I check it and then click 'ok' and then re open the dialog, it isn't checked anymore, and the Load Behavior says "Not loaded. A runtime error occurred during the loading of the COM Add-in The suggested solution using Windows Server 2008 64 bit for same problem does not seem to work. Can anyone help with this problem I have.