Thanks for your reply. This is happening for all decision tables in the application. Each table has different number of rows. I tried this on a decision table with 3 rows and 3 columns. I am using Pega 7.1 version, Internet Explorer11 browser and MS Excel 2016.
Sometimes i am seeing this error 'Switching to NOTEPAD.Exe.There was an error launching application associated with '.xls' file type'. I disabled the option 'Enable Protection Mode' in the security tab in IE settings. Then it started working. Thanks for your support.