I got the following error when using Enterprise Library 3.1. It mean it can’t find the reference to ObjectBuilder or it is resolving to the wrong version in GAC. So to use VAB, you need Common, ObjectBuilder and the VAB assembly. If not that then check this link.
System.TypeLoadException: Method ‘CreateObject’ in type ‘Microsoft.Practices.EnterpriseLibrary.Validation.Instrumentation.ValidationInstrumentationListenerCustomFactory’ from assembly ‘Microsoft.Practices.EnterpriseLibrary.Validation, Version=18.104.22.168, Culture=neutral, PublicKeyToken=21a151ab59c9591d’ does not have an implementation.