VMWare locking out a domain admin account (AP)

Morning Experts,

We have many-a-VMware hosts in our ennvironment, running from a VC with VSphere 4.0 install, but suddenly (without cause) we've seen the VC server locking out on our engineers account, when we see no reason for it, we've found the following error in the logs:


[2011-09-16 09:20:44.541 07776 info 'App'] [VpxLRO] -- BEGIN task-internal-119 --  -- vim.SessionManager.login -- 741083B6-549B-452F-AB9A-DEDA9CC48F4B
 
[2011-09-16 09:20:44.541 07776 info 'App'] Error 1909 authenticating user DOMAIN\Useradmin.
 
[2011-09-16 09:20:44.541 07776 error 'App'] Failed to authenticate user <DOMAIN\Useradmin>
 
[2011-09-16 09:20:44.541 07776 info 'App'] [VpxLRO] -- FINISH task-internal-119 --  -- vim.SessionManager.login -- 741083B6-549B-452F-AB9A-DEDA9CC48F4B
 
[2011-09-16 09:20:44.541 07776 info 'App'] [VpxLRO] -- ERROR task-internal-119 --  -- vim.SessionManager.login: vim.fault.InvalidLogin:
 
(vim.fault.InvalidLogin) {
 
dynamicType = <unset>,
 
faultCause = (vmodl.MethodFault) null,
 
msg = "",
 
}