使用Workbooks.Open读取excel文件时出错，SOS解决思路

使用Workbooks.Open读取excel文件时出错，SOS
。。。。。。
Excel.ApplicationClass   app   =   new   Excel.ApplicationClass();  
Excel.WorkbookClass   workBook   =   (Excel.WorkbookClass)app.Workbooks(Path,  
                  Missing.Value,   Missing.Value,   Missing.Value,  
Missing.Value,   Missing.Value,   Missing.Value,   Missing.Value,  
Missing.Value,   Missing.Value,   Missing.Value,   Missing.Value,  
Missing.Value,   Missing.Value,   Missing.Value);

报如下错误：
An   unhandled   exception   of   type   'System.Runtime.InteropServices.COMException '   occurred   in   excel2txt.exe

Additional   information:   Old   format   or   invalid   type   library.

请问是怎么回事啊，编译没错的阿



[解决办法]
加这个

_Application xlApp = null;
_Workbook xlWorkbook = null;
_Worksheet xlWorksheet = null;
System.Reflection.Missing oMissing = System.Reflection.Missing.Value;