Problem with smfi_setreply

I am trying to create a milter, and everything appears to be working
correctly except for the call to smfi_setreply. I am placing the call first
in my xxfi_evnrcpt function. It does not return an error, but when a
message is rejected, rather than using the custom code that I specified, the
mail server replies with 451 4.7.1 Service unavailable. Could anyone tell
me why this might be? Code is below:

char * rcode = "550";
char * xcode = "5.7.1";
char * message =- "Recipient not found in local address table";

smfi_setreply(ctx, rcode, xcode, message);