Process provisioning for document: Unable to set "pname" "Synchronize Plesk Domain" in for a domain, say, domain2.tld fails with the error:
Process provisioning for document; Unable to set "pname" argument's value ("Client1"): The customer with this name Client1 already exists.
There are two domains 'domain1.tld' and 'domain2.tld' that belong to different clients, "Client1" and "Client2" correspondingly, the Plesk panel. In OBAS those two domains are in different subscriptions which belong to the same customer "Customer".
When OBAS synchronizes the 'domain2.tld' subscription it tries to change its owner to "Client1" in the Plesk panel, but this user exists already. There is no conception of "subscription" in Plesk 9.5, so two different domains of one and the same customer can only share one and the same client.
Create a new customer for the subscription 'domain2.tld' in OBAS and change account for that subscription to the new one, or reassign the domain to Client1 in Plesk panel.