Re: Any update on the status if 64-bit Lightning builds for MacOS/X to be compatible with TB Aurora?

It is just the time of the branch uplift. Thunderbird 19 was uplifted to 
the BETA channel. Thunderbird 20 was uplifted to the EARLYBIRD channel. 
DAILY channel is now Thunderbird 21.

You were trying to combine an old Thunderbird 20.0a1 build from before 
the uplift with a Lightning build from after the uplift that already 
requires Thunderbird 21.0a1.

For current compatibility as of 2013-01-08 see 
https://developer.mozilla.org/en-US/docs/Calendar/Calendar_Versions#Development_Snapshots

According to your Thunderbird version you are on the DAILY channel, 
therefore use the builds from latest-comm-central.