I SOLVED THIS ISSUE:
Please take a look of Software Requirements
* Linux kernel - 2.2.14 or higher with the following libraries or
packages:
o glibc 2.3.2 or higher
o XFree86-3.3.6 or higher
o gtk+2.0 or higher
o fontconfig (also known as xft)
o libstdc++5
(Many modern Linux distributions only package libstdc++6,
which is incompatible with Lightning. Therefore please install the
package "libstdc++5" or "compat-libstdc++" on your system before
installing Lightning)
1) In my case i needed libstdc++5
sudo apt-get install libstdc++5
2)
Lightning 0.7 only allows read mode, so i uninstalled it and installed
version 0.8.
Download from here
http://www.mozilla.org/projects/calendar/lightning/download.html
3)
Now you can install the Provider for Google Calendar.
https://addons.mozilla.org/en-US/thunderbird/addon/4631
Voilá! no more alert on add ons.
More info here:
http://forums.mozillazine.org/viewtopic.php?f=46&t=773665
Regards,