为什么我在我的Excel Addin中“无法在证书存储中找到manifest签名证书”?

I've got an Excel add-in project that was created a couple years back in Visual Studio 2008. It's got some changes to be made so I've upgraded to Visual Studio 2010 (the only IDE I am able to use). Not sure if this is causing the problem but it's background information.I've got an Excel add-in project that was creat