Error with implicit date calculation

I need a hand with SQL. I'm using 9.2.0.4.

I need to compute a date offset by a number of weeks from another date. This is a line from a view that I had been using:

TO_DATE('7-Dec-1998') + (WeekNum * 7) As WeekDate

WeekNum is, of course, the field that contains the number of weeks to offset from the date. This used to work just fine - it doesn't any longer. The TO_DATE function now returns the error:

     ORA_1858 a non-numeric character was found where a
          numeric character was expected

If I change it to TO_DATE('7-Dec-2000') or any later date, it no longer gives an error. It does not return the desired value, of course, but no error. Any date 1999 or earlier causes the error.

I would appreciate any advice how to correct this. Received on Wed Feb 20 2008 - 15:32:35 CST