Can you be more specific on the error message you are getting (screenshot would help) and when you are getting it. Do you logon to vCenter using normal client and web client the same way ? For example, do you logon with IP address or FQDN ?
VCP6-DCV, VCP5, CCNA, MCTS 2008R2, MCSA 2008R2, CCA, ITIL.
Please mark answer helpful or correct as appropriate.