In a report you can refer to fields in the recordsource even if there are no controls bound to those fields. Not sure you can do that on a form - never tried. Regardless, there is no evidence in your post that you have those fields in the recordsource or as controls on the form. If not, you can't use them in your concatenation.
EDIT - Just tested and yes, you can refer to a recordsource field for a form if there is no control on the form that is bound to it. Anyway, that's the question before you. Are your 3 fields part of the recordsource at least? Plus, you have a 2 part problem - circular reference in that expression. Likely one of the elements in the reference is also referencing the same thing. Click on the error and see what info it gives you for the circular reference.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.