Data type of global variable isnt corrispondent with origin

Hi, 
after upgrade to Docuware 7.4 from 7.3, any workflows that use this configuration give this error.

I have a global variable
Name: Firmatari
Type: User of group (list variable)

When a value (user of group) is assigned to variable (without sobstitution), workflow give this error
"Il tipo di dati della variabile globale Firmatari nell'assegnazione della decisione Firme necessarie non corrisponde alla relativa origine".

How can I add a user to that variable?

Thanks

Dear Mayra Rossi! It looks like the Community cannot answer your question. That's why we have opened a Support Request with the Number SR-154472-B3Q6M for you. A Software Support Specialist will contact you directly to follow up. We will update this thread with the solution as soon as we have resolved the Support Request. With best regards, DocuWare Support Team