Excel 2010 AddIn not loaded when Excel-Workbook op

问题:

I wrote a Add-In for Excel 2010. It works fine if I open Excel from Start menu. But just if I double click on a Excel Workbook, the AddIn can not be loaded. I checked it in ThisAddIn.cs, the method InternalStartup() has not been involved. Can somebody help me? Thanks!

But opening file from command line "excel.exe table1.xlsx" works!