problem with google Calendar while upgrading from wicket 1.5 to 6.9

[Piratenvisier]

I am using Google Calendar Service in my wicket application,
which I bring now up to wicket 6.9.
First I had to upgrade to com.google.gdata core 1.47.1
because of other guava dependencies.
When I include the Statement; CalendarService myService = new 
CalendarService("exampleCo-exampleApp-1");
I get the error: java.io.NotSerializableException: 
com.google.gdata.client.calendar.CalendarService

Best regards
H.Braun