problem in reading excel sheet

Question

Hi to all

           I have written a program for reading the contents of the excel sheet..
          
           I have given the condition like

while (((Excel.Range)workSheet.Cells[rowIndex1, colIndex3]).Value2.ToString() != null)
{

           //values of each cell..
}

            It works properly if i have values till row no. 87.. If i include even one more row the loop does not terminate. it keeps on going..

             Can anybody tell me the solution?

With regards

ila