thunderbird error: bad calender item undeletable

[oxy]

Hi,

I had an appointment for 13h, alarm at 12h.
After the alarm i reedited it to alarm 12:45.

The item got bad, cannot delete it anymore,
It keeps showing up reminds every few minutes.

Below the entry. Thunderbird 17.0.2 on ubu 12.04/unity.

Thx for any tipp...

------------ the bad entry ------------

BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/Berlin
X-LIC-LOCATION:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20121213T151051Z
LAST-MODIFIED:20130110T131758Z
DTSTAMP:20130110T131758Z
UID:141ad88c-26f2-4ae2-98d4-b4044801c5bf
SUMMARY:bzzzzzzzzzzzz...
X-MOZ-LASTACK:20130110T131758Z
DTSTART;TZID=Europe/Berlin:20130110T150000
DTEND;TZID=Europe/Berlin:20130110T151000
LOCATION:Raum 25.41.o2.25\, neben benutzerbüro\, F:-15950
DESCRIPTION:bzzzzzzzzzzzzzz...
TRANSP:OPAQUE
X-MOZ-SNOOZE-TIME:20130110T132758Z
X-MOZ-GENERATION:1
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER;VALUE=DURATION:-PT1H
DESCRIPTION:Default Mozilla Description
END:VALARM
END:VEVENT
END:VCALENDAR