I am not sure if this is similar to your case but I had similar problem while using WebLogic with it's feature called deployment plan. Solution can be found in Utils.class inside of antlr itself. They use method getContextClassLoader:
Fortunately there is a switch in this class which let us to disable it:
You have to add to JAVA_OPTS of application server:
-DANTLR_USE_DIRECT_CLASS_LOADING=true
And problem should be gone.
