To reproduce:
Add a RadScheduler and a database with appointments. Set the recurrence rule to the following:
FREQ=WEEKLY;UNTIL=20140102;BYDAY=TH;WKST=SU

A first chance exception will be thrown and the appointments will not show correctly.

Workaround:
Before setting the recurrence rule make sure that the UNTIL keyword's value is in the following format: 20140102T235959Z or more specifically - yyyyMMdd\\THHmmss\\Z