I installed FC 16 and restored my home directory.
There are no entries In thunderbird calender anymore!
Could the reason be that in FC 16 the versions of thunderbird and thunderbird-lightning are older then in FC 15?
FC 15 (2011 Nov 19):
thunderbird-8.0-2.fc15.x86_64
thunderbird-lightning-1.0-1.fc15.x86_64
FC 16 (2011 Nov 20):
thunderbird-7.0.1-1.fc16.x86_64
thunderbird-lightning-1.0-0.50.b7.fc16.x86_64
What to do?