Not quite accurate. The LAN is the network in your house, and people use that word as if you have to be connected to that. You don't.

No cable of any kind, no network adapter, is required to operate the inter-process communication. 

It is not the LAN that is used. The LAN is for computer-to-computer communication, locally within the premises.

It is the loopback TCP/IP stack that is used for application-to-application communication, locally within the one computer, that is needed.

Part of the confusion comes from the fact that the TCP/IP stack is used both for intra-computer communication, and also for inter-computer communication, and that firewalls block both. This does not mean that you need to connect to a network, just because you need to tell your firewall not to block Poser. Further, many firewall programs assume you the user is a technical noob and cannot handle the subtle distinction between the question "Should I let Poser talk to itself" versus "Should I let Poser talk to other computers"? As a result, many firewalls ask "Do you want to give Poser access to the Internet?", the user says no, and the firewall shuts Poser out of the communication stack altogether, not just for reaching the Internet. The result is the library stops working. This has nothing to do with the Internet, but the issue is confused by the nature of the question and the assumed action that was taken as a result of the question. The firewall developers are making a gross mistake by glossing over this distinction and it will come to hurt apps a lot more over time. With new computers having ever more numbers of processors, the technique of using inter-process communication to combine the power of multiple CPUs, either in the same machine, or across multiple machines, is going to be more and more common. Users of software, like it or not, are going to have to understand that telling the operating system what to allow or not allow is going to involve separate answers for "the network inside the machine" versus "the network outside the machine". 

I understand the graphics community is not a bunch of network engineers like me, but if you're going to use the words that network engineers use, such as LAN, then you have to abide by what they actually mean.

Do you need to connect your Poser computer to the Internet? No.

Do you need to connect your Poser computer to a LAN? No, unless you want to use multiple-computer rendering.

You do not need to connect your Poser computer to anything in order to use Poser with the library. Also, some of the 3rd party libraries also use the internal loopback connection and if you block it, they stop working also.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)