I noticed this morning that the Lightning calendar (Ver 0.9) was
missing from my Thunderbird email program (V2.0.0.23). It was there
yesterday I no longer have the calendar icon beneath my listing of
email folders. And, Lightning no longer appears in the Thunderbird
Options screen. Did the usual restart to no avail. In Thunderbird
Add-Ons, I disabled, then uninstalled Lightning just in case there was
some corruption going on. Pulled a fresh version from the internet
and tried to install. Received an error "Thunderbird could not
install the file at (path) because" Unexpected installation error.
Review the error console for more details. -203"

I'm stumped. Any clues anyone? Thank you.