Is there any attribute already added to the audit trail? Or is it the first time you try to add attributes to the audit?
If there are attributes already present, do you get an error when clicking on save without doing any addition?
If so, can you try removing all the existing fields form the audit? Then save the changes so the audit trail is empties and the corresponding trigger removed.
Once done so try to add them again.
If might be a problem with a pre-existing trigger.
Please also check the app-ca.log file to see what it complains about.