I'm dual booting using Linux Mint and Windows 7. I have TB 31.0 installed in each OS. TB in Linux has calendar capability; in Windows, there's nothing (by nothing, I mean no calendars - I can't see their properties, for instance, nor access them in any way). I should add that both Windows and Linux TB programs are sharing the same profile folder (located on a separate partition), hence, all the same add-ons, passwords, etc. The error console logs the following: Timestamp: 14/08/2014 6:41:33 PM Error: Components.classes[cid] is undefined Source File: resource://calendar/modules/calUtils.jsm -> file:///P:/PortableApps/ThunderbirdPortable/Data/profile/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calUtils.js Line: 17 There are a variety of flow on errors, related to this. My apologies for posting this in this way; I had intended to submit this via the crashreporter, but I'm having trouble getting the program to crash with this error just now.