SQL & PL/SQL

I have an input date variable L_DATE as 11-Aug-2013(DD-MON-YYYY).
In my procedure, I am converting the input date to MM/DD/YYYY format .

The logic I have used for the same in my Stored Proc- COMPARE2 is:
R_DATE := to_char(to_date(L_DATE,'DD-MON-YYYY'),'MM/DD/YYYY');

But this is the error that I get when the SP is run:
ORA-01843: not a valid month
ORA-06512: at "COMPARE2", line 51
ORA-06512: at line 2

Can anyone suggest how to resolve this??