java.lang.VerifyError when running grover instrumented code

When certain grover instrumented classes are loaded, the following error occurs at runtime.
Attached is the ContentRepositoryService class.

Error executing script TestApp: (class: org/weceem/services/ContentRepositoryService, method: getAncestors signature: (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object Wrong return type in function
java.lang.VerifyError: (class: org/weceem/services/ContentRepositoryService, method: getAncestors signature: (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object Wrong return type in function
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Class.java:2291)
at java.lang.Class.getDeclaredField(Class.java:1880)
at _PluginDependencies_groovy$_run_closure8_closure70.doCall(_PluginDependencies_groovy:616)
at _PluginDependencies_groovy$_run_closure8_closure70.doCall(_PluginDependencies_groovy)
at _GrailsSettings_groovy$_run_closure10.doCall(_GrailsSettings_groovy:287)
at _GrailsSettings_groovy$_run_closure10.call(_GrailsSettings_groovy)
at _PluginDependencies_groovy$_run_closure8.doCall(_PluginDependencies_groovy:596)
at _GrailsBootstrap_groovy$_run_closure1.doCall(_GrailsBootstrap_groovy:69)
at _GrailsBootstrap_groovy$_run_closure6.doCall(_GrailsBootstrap_groovy:136)
at _GrailsTest_groovy$_run_closure9.doCall(_GrailsTest_groovy:309)
at _GrailsTest_groovy$_run_closure9.doCall(_GrailsTest_groovy)
at _GrailsTest_groovy$_run_closure1_closure21.doCall(_GrailsTest_groovy:193)
at _GrailsTest_groovy$_run_closure1.doCall(_GrailsTest_groovy:171)
at TestApp$_run_closure1.doCall(TestApp.groovy:102)
at gant.Gant$_dispatch_closure4.doCall(Gant.groovy:324)
at gant.Gant$_dispatch_closure6.doCall(Gant.groovy:334)
at gant.Gant$_dispatch_closure6.doCall(Gant.groovy)
at gant.Gant.withBuildListeners(Gant.groovy:344)
at gant.Gant.this$2$withBuildListeners(Gant.groovy)
at gant.Gant$this$2$withBuildListeners.callCurrent(Unknown Source)
at gant.Gant.dispatch(Gant.groovy:334)
at gant.Gant.this$2$dispatch(Gant.groovy)
at gant.Gant.invokeMethod(Gant.groovy)
at gant.Gant.processTargets(Gant.groovy:495)
at gant.Gant.processTargets(Gant.groovy:480)
Error executing script TestApp: (class: org/weceem/services/ContentRepositoryService, method: getAncestors signature: (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object Wrong return type in function