Hello,
the error 704 is probably due to a data file not found. You can see the error message associated with a Mascaret instance (id) calling the scilab function :
[erreur,message]=getErrorMASCARET(id)
This function is not yet documented in the Scilab help.
For the other question, you can have in Scilab a description of all the variables using the function 'getDescVarMASCARET'. This function is documented in the Scilab help.
Alternatively, you can also read the API documentation in .pdf format given with the Fortran sources of Mascaret (only in french).
Regards