I never used the Serena model. The Dagon that I used was version 0.6.5, which was earlier than the Serena version. However, maybe the reasons for getting a black node might be the same with both versions.
Most possible reason is a typing error in your LUA file, including misplaced punctuations. This was most often the case when I got a black node. Check your switch especially. Make sure your switch lists the exact name of the room file. Also, if the destination room file is broken, you get a black node on the switch.
Your TEX files should be exactly 12,289kb each. If they are not that size, then try running them through ksconnect again. Sometimes there would just be a glitch in creation. Or, there might be transparency in one or more of your TGA files. If so, remove the alpha and run the node's TGAs through ksconnect again. Finally, make sure that all six of the TGAs for that node were in the folder.
These seem very basic, but I can't tell you how many times I did just these things.
I hope this is of help.