Deploy jobs created in 5.3 and above app servers will not work against against pre-5.3 agents. To deploy things to an agent using a 5.3+ app server, the agent needs to be at least a 5.3 agent.
NT4 is definitely not supported for 6.2. I'll see if I can get that info removed and/or added to the downloads section.
Thanks for the reply. Seems I could have a bit of an issue emerging here.