Yes, Robert, all the fields are numeric. I did test with the space and without space, and always get the same error. In fact, the expression works with and without the refered space before the AND operators whenever the fields involved are type double. When I include the search in a LONG INTEGER is when I get the error.
If I have 4 fields: municipio (long integer), poligono (double), parcela (double), recinto (double). All my expressions work perfectly with all the conbinations of the double fields. Several multifield searches works without problems. However, the simplest expression across the long integer field produces the error (even if isn't a multifield expression). That is, it works perfectly until I include a long integer field.
I will do more testing but I am running out of options...