adding ESXI server to domain

Hi,

when trying to add esxi version 5 server to domian with the creditional of administrator of  ad domain the esxi server always complain can't add this to domain.we are able to ping to ad domain also and able to telent on port 389 which means firewall is not block.

now the question is where to look the log or from where to start this.

Thanks

D.J.M