ORA-01858: a non-numeric character was found where a numeric was expected

This error occurs if a wrong value is passed when converting a number or string to date. To fix this problem, find out what date format the date is stored in e.g. yyyymmdd, dd-mm-yy, dd-mon-yy, etc. Then rewrite the to_date() statement with the correct format. For example

to_date('11-11-2011', 'DD-MM-YYYY')