Hi Mister Paul,
I believe I can help.
First off: be sure to read this document carefully. You'll avoid a lot of common headaches: Best Practices for LiveUpdate Administrator (LUA) 2.x (http://www.symantec.com/docs/TECH93409)
By default, LUA is designed to install with as wide a compatability as possible. After installation most admins can see great improvements in performance by tuning it for their specific environment. Read the following for more: LiveUpdate Administrator 2.2 Performance Tuning (http://www.symantec.com/docs/TECH96391)
What exactly is happening when the downlaods are failing? Does the following article match what you are seeing? If so, please use the tuning workarounds included in the document: they have led to great improvement for many users. Intermittent "Package is not trusted" errors for various product update files during LiveUpdate Administrator 2.x download phase (http://www.symantec.com/docs/TECH141217)
Final note: there is a new LUA 2.3 which will be released in coming weeks. This new release has a great many performance improvements, fixes (including the one above) and efficiency and usability enhancements. It is a "must have" for all LUA users. Keep a look out for it!
Please let the forum know if this solves your issue or if there is anything additional the community can do!
Thanks and best regards,
Mick