Are you trying to reference from the COM components tab or by browsing?
This page (http://msdn.microsoft.com/en-us/library/vstudio/wkze6zky.aspx) has some information regarding adding COM components:
"If you want to add a reference to a registered COM DLL that contains an internal manifest, make sure that you unregister the DLL first. If you do not, Visual Studio adds the assembly reference as an ActiveX Component instead of as a native DLL."
Hope this is somewhat helpful.