We haven't received reports for such an error before, but there are a few other cases which can cause problems when Exporting to PDF described here
If the problem persists, please provide more details on your implementation such as what server do you use to host your application and do you use AppointmentTemplate. If you can send us a simple working demo of the issue via a support ticket, that would be helpful too.
All the best,
the Telerik team
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