Dear colleagues,
Quick post to document to a simple error in a Italian localization.
If the user tries to launch the VAT settlement and receives this error:

Well, you probably can see in the menu "Tax - Declarations - Sales tax - Settle and post sales tax" that :

The user might have launched the process but not finished it. I know that this field gets populated once you start the settlement. How does the period doesn't get closed and the process is blocked by the user ad vitam eternam? This I don't know.
However, delete the user from the form, save and ask to launch again, this should work.
Hope it helps!
Best regards,
Thomas