Many users have reported problems with using the calendar when allowing users to send WebCards at a future date. I have fixed this bug by updating the calendar file.
I have fixed the calendar.php file in the /tools/ folder. Download the patch from the tracker or re-download the main webcards archive to obtain the updated file.
Once you have uploaded the calendar.php file to the /tools/ folder you can delete the calendar.php file in the /source/modules/ folder.
Please feel free to post a comment or open a bug report if you have any problems or questions.