Re: What causes some threads/topics to gain the "lock" feature?
any one with guru status or admin status can lock a topic for any reason
normal reasons are as you say topic is resolved or is starting to get inappropriate
other reasons are cross posting (posting same exact text over more than one forum) or a topic that really has nothing to do with the forums or a topic that leads to a bad site (trojan, spyware, porn, and etc.) also a topic and user can be locked from posting if the user is causing more problems than they are helping (flamers)
hope this clears some confusion up
(c)robdog 2010 (picture & SN)
(please note) As users we can't give others help unless we get full details of the problem that you are having