GMNL model

Dear STATA users,

I am trying to run a GMNL model using this commands:

gmnl choice rand(espresso highcalories italy highprice) group(setid) id(id) nrep(100)

but I got this message:
"factor variables and time-series operators not allowed
r(101)"

Please, any suggestion on how to deal with this?

Thanks

Daniele