The same user name should not be a problem, as long as you do not attempt to access the server with two different user accounts at the same time from one client.
Would the connection work, if you directly access a shared folder?
Are there any stored user names and passwords on the client for the connection to that server, which do not match the current user?
Eventually did you use fast user switching on the client (although I am not sure, if that would have influence) and this is causing side effects?
Did you rename the user account in the past (according to
this FAQ)?
Best greetings from Germany
Olaf