Hi List, Seems like GWT can't handle Arrays.asList not very well. Sharing this in case others have similar issues: I was working on a very strange deserialization bug in combination with GWT [1]. We had a deserialization problem after loading a VM and trying to send the VM back to the backend. The error looked like this: 2016-06-28 12:17:36,206 ERROR [io.undertow.servlet] (default task-58) Exception while dispatching incoming RPC call: java.lang.NumberFormatException: For input string: "undefined" It turned out that GWT could serialize an ArrayList backed by an Integer[] array but it could not deserialize it afterwards. In my case a list returned by ResultSet#getArray in the DAO layer was sent to GWT: entity.setCpuIds(Arrays.asList((Integer[]) rs.getArray("cpu_core_ids").getArray())); After copying the content over into a regular ArrayList everything worked fine again. entity.setCpuIds(new ArrayList<Integer>(Arrays.asList((Integer[]) rs.getArray("cpu_core_ids").getArray()))) Here is also the gerrit patch set [2]. So if you see strange GWT RPC errors like the one above look out for "Arrays.asList" in you code :). Best Regards, Roman [1] https://bugzilla.redhat.com/show_bug.cgi?id=1350861 [2] https://gerrit.ovirt.org/#/c/61038/2