Did you ensure that you created the account in MVM as well? KB55032 notes that you need to create the account in MVM and it sounds like the User does not exist is referencing that the user you are trying is either not a valid account or does not exist in either AD or MVM.
fter Vulnerability Manager has connected to Active Directory for authentication, you must add the user name to the organizations using the GlobalAdmin account to provide access rights to the Vulnerability Manager system (for more information, see the Vulnerability Manager Product Guide, Create a user section).
After you have created the user, you must provide a password, but it is not used unless the Active Directory integration is removed. The GlobalAdmin user can change passwords within Vulnerability Manager at any time. Changes to the password in Vulnerability Manager do not alter the password for the user within Active Directory.