Ahh, I think I know what's going on.
LuaBind is trying to store a metatable for a table, and the metatable
contains an __eq metamethod which is a C-function. Pluto, which has no
way of serializing C functions, thus fails.
Have you tried adding the metatable to the permanents table? Assuming
there's only one metatable per class, this shouldn't be much overhead,
and should work fine. Tell me if you need help with this; I'd very
much like to be aware of interactions between Pluto and binding
libraries like LuaBind.