There are a number of places where Rcpp can fail becauseTYPEOF(x) does not equalRTYPE. Since both of these are known at the point that the error is given it would help if these were displayed, e.g. rather than just"some message" use:std:string("some message TYPEOF(x): ") + CHAR(Rf_type2str(TYPEOF(x))) + " RTYPE: " + CHAR(Rf_type2str(RTYPE))
At least that will give some bit of clue as to what the problem might be.

Any other info that might be added to the error message to help locate the problem could be helpful too.

This applies to RcppEigen too.