HI Suresh,
The error is mainly because of the work schedule rule assigned to the employee. As you told monday to friday is working day for the employee fine and then as Saturday and Sunday is holiday or non-working day when you are making an entry in 2001 infotype system would throw an error because 05-04-2013 is non working day.
And check in table V_T554S against the absence type whether the reaction indicator is maintained as E for Last Day off. So the message is based upon this setting.
Regards,
Mithun K