Problem:

While working with the report source and column names somehow it became “corrupted”, it was impossible to change the name of one of the columns though possible to update the source and the rest of column names:

While saving the report APEX was showing the bellow error:

_   Error saving column settings with ORA-01403: no data found Error_

Solution:
Try to force APEX to refresh the column names by selection:

(this action will erase all existing column names)

_   Use Generic Column Names (parse query at runtime only)_