It is a little particular in how it expects the value to be set. You are missing a space that is causing the error.
Instead of:
$CKEditor_initialValue = "".((isset($_GET["invalid"])?ValidatedField("eventsbrannualupdate","late_fees_entry_deadline",true):"".$WADAevents_br_annual_update->getColumnVal("late_fees_entry_deadline",false)."")) ."";
it needs to be:
$CKEditor_initialValue = "".((isset($_GET["invalid"])?ValidatedField("eventsbrannualupdate","late_fees_entry_deadline",true):"".$WADAevents_br_annual_update->getColumnVal("late_fees_entry_deadline",false)."")) ."";
I can see you only have one space before the final ."", and there needs to be two spaces.