Error in IT Calculator for HRA Exemption FY 2011-12

Hello Batra Sir, Your Income Tax Calculator for FY 2011-12 is extremely useful for all salaries employees. Thank you very much for providing the same. Sir I found a minor error that HRA exemption for the month of April & May 2011 in not coming correctly. 1).For April 2011 - It comes Nil always & 2) For May 2011 - it comes as #REF! error. Please make necessary amendment in the IT Calculator and provide to help us better. Thanks