Cannot read emails anymore after calendar is activated

Hi,

I activated the plugins 'calendar' and 'libcalendaring' - calendar seems to work correctly, anyway afterwards email content is not displayed anymore - instead the following error is shown in the message window:

Fatal error: Class 'Sabre\VObject\Property\Text' not found in /roundcube/plugins/libcalendaring/libvcalendar.php on line 1385

Any ideas how to solve this? thx,

Robert