The request failed because the remote server 'vCenter' took too long to respond. (The command has timed out as the remote server is taking too long to respond.
This is a known issue in vCenter Server 5.1 and has been resolved in vCenter Server 5.1.0b.
To work around this issue for the vSphere Client, manually enter user credentials when logging in and do not use the Use Windows session credentials option.
To be alerted when this document is updated, click the Subscribe to Article link in the Actions boxActive Directory users with customized UPN user names cannot use Windows session credentials to log into the vSphere Client or vSphere Web Client