Error when using the Date function: "ORA-01843 not a valid month". (4329640)

Error when using the Date function: "ORA-01843 not a valid month".

The NLS settings for the session, instance or database are wrong.

1. Check for the NLS settings:
If using the Quest DBA module of Toad for Oracle,  check the NLS settings by the following:
a. Select Database | Administer | NLS Parameters menu option
b.  Verify the NLS settings under  Session | Instance | Database tab
 
Otherwise execute the following query:
Select * from v$NLS_parameters;  

2. To change the Date format for the session execute the following query:
Alter session set nls_date_format='<required date format>';  

3. Verify if there are  any differences between using it  within Toad for Or SQLPlus (Editor | Execute SQL via SQL*plus)