Lightning 2.6: GCal CalDAV doesn't work anymore

Hi,
after updating to SeaMonkey 2.21 and updating Lightning to version 2.6
Google calendars accessed with CalDAV don't work anymore. This is the
error I get:

Error code: 0x80570015
Description:
[Exception... "Component returned failure code: 0x80570015
(NS_ERROR_XPC_CI_RETURNED_FAILURE) [nsIJSCID.createInstance]"  nsresult:
"0x80570015 (NS_ERROR_XPC_CI_RETURNED_FAILURE)"  location: "JS frame ::
resource://calendar/modules/calUtils.jsm ->
file:///home/iacopo/.mozilla/seamonkey/xxxxxxxx.default/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calCalendarManager.js
:: cmgr_createCalendar :: line 474"  data: no]

I don't know if this happens only to me or if it's a bug. These are
other users with the problem anyway:
https://bugs.launchpad.net/lightning-exchange-provider/+bug/1227617
http://forums.mozillazine.jp/viewtopic.php?f=24&t=14302

bye,
Iacopo