vmError: Save failed with the following error: Username in use.

[MKI-Miro]

Hi

I have migrated virtuemart from 1.1.9 to 3.2.2 using VM Migrator.

In backend Shopper infromation I have empty field Shopper Number / ID:

When i want to save shopper infromation page i get error vmError: Save failed with the following error: Username in use.

How can i fix it ?

Thanks