If you are using Grails Web Flow and put domain object in flash scope.
flash.model = new MyModel()
Make sure your events beforeInsert, beforeUpdate, beforeDelete, etc. are marked transient. Otherwise the domain object cannot be serialized and you get the following exception:
Could not serialize flow execution; make sure all objects stored in flow or flash scope are serializable; nested exception is java.io.NotSerializableException
This happens because closures cannot be serialized.
Always mark your closues as transient to avoid future serialization problems.
class MyModel implements java.io.Serializable {
transient def beforeInsert = { … }
}