Problems importing an calendar event into iCal
There is no end time for the entry so you need to add this into the file.

DTEND:20120830T155000


The ICS specification also states


  the "UNTIL" recurrence rule parameter MUST be used to specify the
          last valid onset of this observance (i.e., the UNTIL date-time
          will be equal to the last instance generated by the recurrence
          pattern). It MUST be specified in UTC time.


so your RRULE line should read:

RRULE:FREQ=WEEKLY;UNTIL=20121212T150000;WKST=SU;BYDAY=MO,WE,FR