[Rcpp-devel] Error with sugar dnorm;

I'm having a problem with sugar expressions that I can't figure out.
I have these two functions that are sampling and prior functions for
two different parameters of an MCMC model.  BTW this is part of my big
CUDA project, so I pass these as pointers into other functions.
---
numeric rb1(numeric a, numeric b){return Rcpp::rbeta(1,a,b)[0];}
numeric pr_trans(numeric x){return Rcpp::dnorm(x,0.0, 1024.0)[0];}
---
the first works fine but the second gives a compile error that

error: no matching function for call to ?dnorm4(numeric&, double, double)?

numeric is typedef double.   I don't see why this fails.  Any ideas?

thanks,
Andrew