During a restore you receive the error message:
“Failed to connect to vCenter server”
The account Veeam Backup & Replication is using is most likely locked out or the password has changed.
Please refer to this KB to find out how to discover which account Veeam Backup & Replication is using to communicate with the VMware vCenter Server. http://www.veeam.com/kb1900
Check if the account that Veeam Backup & Replication is using to communicate with the vCenter Server is locked out.
Try connecting to the VC using the specific account Veeam is attempting to use.