If you want to use BirdieSync with WCAP calendars, it is necessary to patch Lightning or Sunbird to correct some issues.
Download calWcapCalendarItems.js and after backuping the original file close Thunderbird or Sunbird and install it in:
Thunderbird:
C:\Documents and Settings\<users name>\Application Data\Thunderbird\Profiles\<profile id>\extensions\{e2fda1a4-762b-4020-b5ad-a41df1933103}\js
Sunbird:
C:\Program Files\Mozilla Sunbird\js
This patch was released for Lightning and Sunbird 0.7. Don't use it with another version.