[Rd] Dynamic list creation (SEXP in C) returns error "unimplemented type (29) in 'duplicate'"

[George Vega Yon]

Dear R-devel,

A couple of weeks ago I started to use the R C API for package
development. Without knowing much about C, I've been able to write
some routines sucessfully... until now.

My problem consists in dynamically creating a list ("L1") of lists
using .Call, the tricky part is that each element of the "mother list"
contains two vectors (INTSXP and REALEXP types) with varying sizes;
sizes that I set while I'm looping over another list's ("L1") elements
 (input list). The steps I've follow are:

FIRST: Create the "mother list" of size "n=length(L0)" (doesn't
change) and protect it as
  PROTECT(L1=allocVector(VECEXP, length(L0)))
and filling it with vectors of length two:
  for(i=0;i<n;i++) SET_VECTOR_ELT(L1,i, allocVector(VECSXP, 2));

then, for each element of the mother list:

  for(i=0;i<n;i++) {

SECOND: By reading this post in Stackoverflow
http://stackoverflow.com/questions/7458364/growing-an-r-matrix-inside-a-c-loop/7458516#7458516
I understood that it was necesary to (1) create the "child lists" and
protecting them with PROTECT_WITH_INDEX, and (2) changing its size
using SETLENGTH (Rf_lengthgets) and REPROTECT ing the lists in order
to tell the GC that the vectors had change.

THIRD: Once my two vectors are done ("id" and "lambda"), assign them
to the i-th element of the "mother list" L1 using
  SET_VECTOR_ELT(VECTOR_ELT(L1,i), 0, duplicate(id));
  SET_VECTOR_ELT(VECTOR_ELT(L1,i), 1, duplicate(lambda));

and unprotecting the elements protected with index: UNPROTECT(2);

}

FOURTH: Unprotecting the "mother list" (L1) and return it to R

With small datasets this works fine, but after trying with bigger ones
R (my code) keeps failing and returning a strange error that I haven't
been able to identify (or find in the web)

  "unimplemented type (29) in 'duplicate'"

This happens right after I try to use the returned list from my
routine (trying to print it or building a data-frame).

Does anyone have an idea of what am I doing wrong?

Best regards,

PS: I didn't wanted to copy the entire function... but if you need it
I can do it.

George Vega Yon
+56 9 7 647 2552
http://ggvega.cl