I know this error message is really not friendly!
The most important thing to get out of the error is that it is for the calculate for the Culture_Hiv_secH_label field.
If you look at the second to last paragraph, you'll see a [2] next to Prod_parcelle_Hiv. This means that Prod_parcelle_Hiv is a repeat and so you need to either access fields from it within that same repeat or you need to specify which of the repeat instances you want.
Hopefully that gives you some useful hints. If you'd like more advice, you will need to tell us more about the structure of your form or ideally share it.