Ok... So this might not be your case, but throwing it out there. Was chatting to a teacher friend .. she said she ended up having a revenue audit! The one area where she had messed up, was she had claimed for salary protection. However, as this is often (not always) through Cornmarket (and they get over €12 per fortnight for the service), salary protection tax credit is organised at source. She ended up claiming twice for it.
So if your salary protection through Cornmarket, already claimed for.
It might not be...