Check to see what your setting for NLS_DATE_FORMAT is. By default, it is 'DD-MON-RR' or 'DD-MON-RR' (depending on the version you are using). If this is the case, then your query should have worked. However, if you have a different setting (e.g., 'Month DD, RRRR'), then you have to either rewrite your query to use this format or use the to_char function to specify your desired format.

You might want to do something like
SELECT DISTINCT regdate FROM user_details;
to see if there is indeed an entry with the date you are providing in your query. It's possible that there are no rows that match your criteria (in which case, No Rows Returned is exactly right!).