I know its a bug forum, but I have had a relatively smooth ride so far since installing and thought I'd share some tips that may help.
Two main ones really.
1st, if you have Windows Vista, DISABLE User Account Control.
this is just a general thought. Its solved countless problems for me before.
Best if done BEFORE installation.
2nd, ALWAYS check to make sure windows firewall has an exception for the STO client.
Mine didn't and it solved several errors when added.
3rd, after enacting these two changes, REBOOT before relaunching STO.
Not sure if this will help, but I hope it works for someone.
# 2 has been known to solve the 'Unable to authenticate' Message in my case and another persons.