I had a similar issue. Are you entering a date as a parameter field?
That was my case and I had to enter my date in this format:
yyyy-mm-dd
OR
If you are using a SQL command for your report and defining which date to use in your SQL; I think you could either use 'yyyy-mm-dd' or (ex.)'12-DEC-00'.
I am not too familiar with Oracle, but this was how I got around the error you are getting.
You could also use the 'to_date' function in your SQL:
WHERE date = to_date('2002/12/18','yyyy/mm/dd')