My dependent variable has four categories, including 1) working & studying; 2) working but not studying; 3) studying but not working; 4) not working and not studying. I use the command "mprobit" to run multinomial probit regression as follows:

mprobit Work_studycross ib1.SEX ib1.Sex_HeadHH ib1.RE_SEC_head_nomissing ib1.Occu_headrecode ib1.Occuhighestnonheadrecodenochi ib3.Edu_head4groupsfinal ib4.EduhigestnonheadnochildeduFIN ib2.AREA ib0.Have_child0to14years ib1.Have_adult ib2.Family_disrupt ib2.TypeHH_relationtohead , baseoutcome (4)

Then, I managed to obtain the table that has four sections which the first section is for Outcome 1 while the last section is for Outcome 4. This table has coefficient and standard error. So I try to use the command "mfx, predict(pr outcome(1))" as I want to obtain the table with marginal effect. However, the result is that there is no independent variables (as shown in the bold texts below). What does this mean? And what should I do to obtain mariginal effect for multinomial probit?

. mfx, predict(pr outcome(1))
no independent variables
r(102);

(Note: I use the command "tab" to check the number of observations in the independent variable, and I found that there are observations for all four categories of the independent variables, such as category 1 = 374 observations, category 2 = 552 observations, category 3 = 6,666, and category 4 = 510 observations which cateogry no.4 is my baseoutcome (reference group)

Many thanks in advance for your advice
Kanoknit