Creating the same user in both computers works for desktop OS like XP or 7, but not for domains.
Since you are using a domain, you need to create the user in the domain, not local users in both computers (if you don't use it I don't think that you can use Windows authentication, since that doesn't provide enough security).
The whole point of a domain is having a single set of users so you can set permissions easier for all the computers and resources of the domain.
Also, check that the network connection is properly configured (we have problems in our office network because some computers didn't use the domain server as the gateway, which is needed in our domain configuration).