提示Excel.Range的select()方法无效

根据dataset的两个表分别添加到excel的两个sheet中
下面是画表格语句，但在执行第二个sheet时提示错误Excel.Range的select()方法无效
代码如下：
int sheetCount=2;
for(int i=1;i<=sheetCount;i++)
{

m_oMissing = System.Reflection.Missing.Value; if(ds.Tables[i-1].Rows.Count==0)
{
}
else
{

workSheet = (Excel.Worksheet)workBook.Worksheets[i];



Excel.Range r=workSheet.get_Range(workSheet.Cells[top-1,left],workSheet.Cells[ds.Tables[i-1].Rows.Count+top-1,ds.Tables[i-1].Columns.Count+1]);

r.Select();
app.Run("宏1",m_oMissing,m_oMissing, 
 
m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing, 
 
m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing, 
 
m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing, 
 
m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing,m_oMissing); 


}
}