Authentication error when using jbpm rest enpoint at BC

When accessing to jbpm pages (process instances, tasks,..) that executes dataset queries an Authentication Exception is thrown:21:35:24,670 ERROR [stderr] (default task-2) java.lang.IllegalArgumentException: object is not an instance of declaring class
21:35:24,671 ERROR [stderr] (default task-2) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
21:35:24,671 ERROR [stderr] (default task-2) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
21:35:24,671 ERROR [stderr] (default task-2) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
21:35:24,671 ERROR [stderr] (default task-2) at java.lang.reflect.Method.invoke(Method.java:498)
21:35:24,671 ERROR [stderr] (default task-2) at org.jbpm.workbench.ks.security.KeyCloakTokenCredentialsProvider.getAuthorization(KeyCloakTokenCredentialsProvider.java:64)