LP:
Unfortunately, this is the case. I don't have the details of their disagreement; although, I'm sure that someone will likely bring that topic up... The bottom line is that you will have to register Poseidon seperately from your Spider-II.
On the plus side, neither Elbox or Posiedon's author take their grudge out on the customer. They are both very helpful, even if they do not agree with one another.