Showcase grid cell widgets not serializable

[futtegud]

I have a TreeGrid where I have used cell widgets like in the showcase example at:

http://www.smartclient.com/smartgwt/showcase/#featured_grid_cell_widgets

but it gives me the following error when I try to send data to the datasource:

00:19:25,915 [ERROR] 19:03:03.785:KPR5:WARN:JSONEncoder:Attempt to serialize class of type: HLayout at path: .id.ucId.step.action.subTransaction.parentTransactionId.isFolder.transIndex.$29a[0] - returning null for this slot.

com.smartgwt.client.core.JsObject$SGWT_WARN: 19:03:03.785:KPR5:WARN:JSONEncoder:Attempt to serialize class of type: HLayout at path: .id.ucId.step.action.subTransaction.parentTransactionId.isFolder.transIndex.$29a[0] - returning null for this slot.
 	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
 	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
 	at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
 	at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:105)
 	at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
 	at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:157)
 	at com.google.gwt.dev.shell.BrowserChannel.reactToMessages(BrowserChannel.java:1668)
 	at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:401)
 	at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222)
 	at java.lang.Thread.run(Thread.java:619)

It seem to be the HLayout that I have used for the cell widgets, just as shown in the showcase example. It seems not to be serializable and that is what is causing the error. Is there some way to serialize it or not send it at all?