HumanPlayer humanPlayer;
            if(args.Length > 0)
            {
                ulong targetId;
                if (!ulong.TryParse(args[0], out targetId))
                {
                    SendReply(player, "/npc_add [TARGETID]");
                    return;
                }
                HumanNPCInfo tempInfo;
                if (humannpcs.TryGetValue(targetId, out tempInfo))  //Patched...  Line 2587
                {
                    SendReply(player, "NPC Already Exists..");  //Updated  Line 2589
                    return;
                }
                humanPlayer = CreateNPC(player.transform.position, currentRot, "NPC", targetId);
            }


// Before 
            HumanPlayer humanPlayer;
            if(args.Length > 0)
            {
                ulong targetId;
                if (!ulong.TryParse(args[0], out targetId))
                {
                    SendReply(player, "/npc_add [TARGETID]");
                    return;
                }
                HumanNPCInfo tempInfo;
                if (!humannpcs.TryGetValue(targetId, out tempInfo))  // ! wrong. <Current Line 2587
                {
                    SendReply(player, "Couldn't find the NPC");  // Current, wrong error msg  Line 2589
                    return;
                }
                humanPlayer = CreateNPC(player.transform.position, currentRot, "NPC", targetId);
            }

Couldn't use the latest version on umod until the chat command npc_add was patched. Posting just in case anyone else had the same issue.  Version 0.3.45

The /npc_add is for new npc  /npc_add <idhere> is to clone an npc.

NPC_ADD
Creates a new NPC, and edits it.
It will be created where you stand, and be looking the same way that you are. Using /npc_add XXXX (npc ID from /npc_list) will clone the NPC to your position

I love this plugin its very good for servers.
Only problem i ever ran into with it is recently when trying to use this and raidable bases it crashes my server for ram overload spikes over 15mins intervals.

Not exactly sure why, but i do see a recent update and i may try this plugin again because i miss using it for different things, it can make a server look/act and feel different.

Thanks to Ts3hosting for maintaining this plugin