ORA-01839 date not valid for for month specified error message

 Okay, the challenge is to try and describe my issue clearly. I am wanting to write an SQL statement and in that statement I am needing to compare the value of a character field to a date field.  The WHERE clause that I am specifically doing is this -

TO_DATE(bv1.version_name,'MM/DD/YYYY') <= wip.pa_date

VERSION_NAME is my character column/field.  It is intended to hold a date type value, in the specified format (for example, a value = '05/31/2010').  Of course this being the real world and an alpha field, the contents of this column often don't match the desired format.  So I added some more stuff to the WHERE clause -