I had a look at your database structure and I think you are going on a wrong path.
First of all you should not use lookup fields in the tables (you have many of them in the TbSentieri table), see the following link for explanations: http://access.mvps.org/access/lookupfields.htm (more at http://access.mvps.org/access/tencommandments.htm). Users should not be allowed to open your tables directly so remove the lookup fields and use combo boxes in the form(s). You will have to reset your relationships while doing that. The "lookup" tables will be referenced in the row source of the combo boxes but the control source of the combo will be the corresponding field in the bound table. These "lookup" tables should not duplicate the information (TbDifficoltà, tbZone, etc.) should only have one record for each value, not multiple as you have it now.
I have started to fix it, I have removed the lookup fields for Zone, Difficolta and Origine. Then in the MsInserimentotoDati form I have removed the three tables from the record source as they are not needed there. Finally for the three combos I set them up to have 2 columns, first one (the bound one) being hidden (set column widths 0";3") added the Id field to the row source and removed the group by.
I wanted to leave the rest to you so you can learn how to do it, please let me know if you have any questions.
Sorry but if you have patience let's do it step by step otherwise explain us only with messages for me that are not up to the situation it becomes really difficult it would be easier to see it than to apply it but since it is not possible let's do it slowly so I understand.
So first you tell me that I have to remove from the table in particular that of the Paths all the search combo boxes and replace them in the "text box" then restore the relationships.
I'm sending you the file to see what I've done.
I didn't understand what to do afterwards I looked at the whole database.
Good evening and always Thank you. Montagna.zip
Sorry for the delay in getting back to you! Please have a look at the updated file, you should have the explanations on what I have done to it in my other message.