Hi Pradeepac,
I tried with following test code and it works fine.
Workbook wb = new Workbook();
Cell cell = wb.Worksheets[0].Cells["a9"];
cell.SetAddInFormula("ATPVBAEN.XLA", "=YIELD(\"05/09/2006\",\"03/12/2007\",0.0539000000,101.2945148936170213,100,4,0)");
cell = wb.Worksheets[0].Cells["a15"];
cell.SetAddInFormula("ATPVBAEN.XLA", "=YIELD(\"05/09/2006\",\"03/12/2007\",0.0539000000,101.2945148936170213,100,4,0)");
cell = wb.Worksheets[0].Cells["a10"];
cell.SetAddInFormula("ATPVBAEN.XLA", "=YIELD(\"05/09/2006\",\"03/12/2007\",0.0539000000,101.2945148936170213,100,4,0)");
wb.Save("d:\\test\\abc.xls");
Could you please post your code to reproduce this problem? Thank you very much.