You will need to add the reference from the Primary Interop Assemblies. In Visual Studio, click Project, and then click Add Reference. In the Add Reference dialog box, click the Browse tab. Go to "C:Program FilesIVI FoundationIVIBinPrimary Interop Assemblies" and locate four dll ITLTYPELIBLib.dll Ivi.Driver.Interop.dll Ivi.Scope.Interop.dll TekScope_TektronixLib.dll