When you build a managed Office extension of any kind, you should ensure that your extension is isolated from other extensions that might be loaded into the application. You do this by creating a custom shim. VSTO solutions do not require custom shims because the VSTO runtime includes default shim functionality. However, if you are writing your own managed shared add-in you will need to write your own shim.
The COM Shim Wizards automate the generation of COM shims for managed shared add-ins. Now that Office 2010 ships with a 64-bit version you’re probably wondering how to support it in your shared add-ins. If you’re using these wizards then you’ll want to read Misha’s latest post on how to get a working 32-bit shim wizard to work with 64-bit of Office. Thanks Misha!
–Beth Massi, Visual Studio Community