Catch 'ItemCannotBeLockedException' when state=Released

Hi, I'm trying to figure out how and where to catch the Aras.Server.Core.ItemCannotBeLockedException exception so I can display a custom error message to the users.  The executed AML is: <Item type="MyCustomDocument" id="123134234234" action="lock" />. I have implemented "OnBeforeLock()" on my custom ItemType, but this method isn't hit when the ItemType is in Released state. So the question is at which stage in code is the exception thrown and can I sort of catch it or handle it?