I am trying to run a existing project which uses 'Microsoft Office 12.0 Object Library' with Version 2.3.0.0 which is I think. Just to be safe, I downloaded the Office Primary Interop Assemblies and reinstalled them. You need to use an object library for the version of Office you have. It sound like you don't have Excel 2007/Access 2007 installed on your. Free source code and tutorials for Software developers and Architects. knew the filename because there are about 50 different DLL's in there. Just before posting, scroll down to GO ADVANCED, click, and then scroll down. I'm running Excel 2007 on a Windows 7 machine and when I open the.