Hello,
IPlease check these Threads with similar issue:
https://www-secure.symantec.com/connect/forums/live-update-server-stopped-downloading-definition-files
https://www-secure.symantec.com/connect/forums/liveupdate-administrator-always-failed-download-updates
https://www-secure.symantec.com/connect/forums/liveupdate-administrator-download-fails-every-time
Secondly, I recommend upgrading the version of LUA that you are using:
LUA version is 2.3.0.71.
I recommend upgrading to LUA 2.3.1, and installing it fresh on a server that does not have a SEPM installed. That should work fine.
Here are a couple articles about LUA that may help:
https://www-secure.symantec.com/connect/articles/managing-liveupdate-administrator-2x-space-usage
https://www-secure.symantec.com/connect/articles/helpful-liveupdate-administrator-2x-analogy
To grab the Latest LUA 2.3.1, you could either Download the Latest DVD of SEP 12.1 RU1 MP1 .i.e;
Symantec_Endpoint_Protection_12.1_RU1_MP1_Part2_Tools_and_Documents_EN.exe
...Tools\LiveupdateLUAESD.exe
OR
Create a Case with Symantec Technical Support.
How to create a new case in MySymantec (formerly MySupport)
http://www.symantec.com/docs/TECH58873
Please do keep this thread up to date with your progress!