The serial number cannot generate for some items

Summary:

Hi ,

I want generate the serial number for an item.

But I have this error: "You cannot generate the serial number because the starting serial number is not defined, incorrectly defined, or currently in use."

The set up in the task "manage inventory organization is :

while the set up in Product management for used items is :

The serial number generation doesn't work for same items with the configuration in the imagines.

Thanks

Best regards

Michela