Because of a design error, field calculator must write on disk over the gvSIG instalation directory. In case that the user who executes gvSIG does not have write permisions over the directory some field calculator options are not loaded so
it is not possible to use it correctly.

Temporarily (untill error is rectified at source) it is possible to avoid the
problem in this way: inside [gvSIG instalation directory]/bin, create a
directory called "cachedir" and inside this one other called "packages". Next time field calculator is run, every functions are right loaded and it is possible to use them without problem.