The error numbers are listed in the header files <rw/coreerr.h> and <rw/matherr.h>. You can see the associated error messages and auxiliary information in files coreerr.cpp and matherr.cpp, and surmise the auxiliary information contained in the va_list. For example, the error RWMATH_INDEX is listed in matherr.cpp as:

The first argument in the va_list is the index the user attempted to use, and the second is the highest allowed index.