SQL & PL/SQL :: ORA-06575 Package Or Function In Invalid State

The function is supposed to tell whether numbers stored as a string value evaluates to a date.I copied into an SQL windown in PL/SQL Developer and typed "commit;" after and then tried to view the results as I posted below to make sure the function worked.

However, I get an ora-06575 Package or Function GETDATE is in an invalid state.So would like to know first, if the code is correct? And if it is, do I need to do something else to make Developer take the code? Here is the code that gave me the error I used to try to test the function:

select GetDate ('010312', 'dd-mm-yyyy')
from dual

Here is the code I used to create the function:

create or replace function GetDate (vDate varchar2, vMask varchar2)
return varchar2
is

vReturnDate date;
begin
vReturnDate = to_date(vDate, vMask);
return vReturnDate;
exception
when value_error then
return 0;
end GetDate;
commit;