DATA VALIDATION - Nonexisting Value When Opening The File

Good afternoon everybody.

I've strange problem.

I've created a drop down menù by a data validation based on a dynamic table, composedby two columns, extracted from SQL.

As the theory requires, I've assigned a name to the first column of the table, the one from whichI takethe values​​of the menu.

The dynamism works...but whe I re-open the file, I found in the cell of the menù a number value that is not conteined in the column...actually it isn't contained in any part of the file!

Then, when I click on the arrow to open the menù, I see all the right elements of the coulomn that I've selected before.

So the problem it's only at the opening of the file.

I've already done this operation before, but I've never seen nothing similar.

Ah, BTW, it isn't a format problem: I've changed the format of the table and of the cell where there's the drop down menù...

Thanks in advance.

Rob