I use Icedove (Thunderbird) since years, and think it's really a good piece of software, in my opinion it's much better than Outlook, I was using for several years too. After splitting up my data into "OS" and "real data", I also moved the .icedove folder from my home directory by symlink to my data-harddisk. Mails worked fine, but lightning would display any evens, you also could not even create any new calendar, events. After I while I saw the following error in the error-console:

Error: Components.classes[This email address is being protected from spambots. You need JavaScript enabled to view it./calendar/datetime;1'] is undefined
Source File: chrome://calendar/content/calUtils.js
Line: 78 

Solutioin: my data-harddisk was mounted by fstab with rw/user (for whatever reason I did this once...), I changed it to defaults what is equal to "rw,suid,dev,exec,auto,nouser,async on my current Debian Wheezy. After rebooting, everything works fine. I really would appreciate if anybody can explain me why this was the solution to my problem.