Sorry I missed your post. I'm running the x64 version of minefield 4.0b2pre.
I'd recommend installing from Minefield by going here: https://lastpass.com/lppre.php
When I go to LastPass Icon -> Tools -> About it shows: Fast Encryption: false
Because we haven't done binary acceleration for it yet, but otherwise it's perfectly fine to use. What problems are you having?
My user agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; Win64; x64; en-US; rv:2.0b2pre) Gecko/20100701 Minefield/4.0b2pre