I switched on debug in iSync (launch it whilst holding down Shift and Option).
vCal to parse: BEGIN:VCALENDAR VERSION:1.0 TZ:+00 DAYLIGHT:TRUE;+01;20100328T020000;20101024T010000;GMT;BST BEGIN:VEVENT SUMMARY;ENCODING=QUOTED-PRINTABLE;CHARSET=UTF-8:= Test=20event UID:511 DTSTART:20100129T125000Z DTEND:20100129T135000Z ATTACH: SEQUENCE:0 LAST-MODIFIED:20100117T123018Z DCREATED:20100117T123006Z END:VEVENT END:VCALENDAR
vCal parsed: { RawProperties = ( { Name = UID; Value = <353131>; }, { Name = SEQUENCE; Value = <30>; }, { Name = "LAST-MODIFIED"; Value = <32303130 30313137 54313233 3031385a>; }, { Name = DCREATED; Value = <32303130 30313137 54313233 3030365a>; } ); "all day" = 0; "com.apple.syncservices.RecordEntityName" = "com.apple.calendars.Event"; "end date" = "2010-01-29 13:50:00 +0000"; "start date" = "2010-01-29 12:50:00 +0000"; summary = "Test event"; }
vCal to parse: BEGIN:VCALENDAR VERSION:1.0 TZ:+00 DAYLIGHT:TRUE;+01;20100328T020000;20101024T010000;GMT;BST BEGIN:VEVENT SUMMARY;ENCODING=QUOTED-PRINTABLE;CHARSET=UTF-8:= Testing=20alarms=20w/log UID:513 DTSTART:20100129T132000Z DTEND:20100129T142000Z ATTACH: SEQUENCE:0 LAST-MODIFIED:20100117T130040Z DCREATED:20100117T130040Z AALARM:20100129T130500 ;PT3M ; END:VEVENT END:VCALENDAR
Failed to parse vCal (1) near index 97: BEGIN:VEVENT SUMMARY;ENCODING=QUOTED-PRINTABLE;CHARSET=UTF-8:= Testing=20alarms=20w/log UID:513 DTSTART:20100129T132000Z DTEND:20100129T142000Z ATTACH: SEQUENCE:0 LAST-MODIFIED:20100117T130040Z DCREATED:20100117T130040Z AALARM:20100129T130500 ;PT3M ; END:VEVENT END:VCALENDAR