Forum Moderators: phranque
Unless . . . they can actually get to the site and just can't log in. This may have to do with cookies and how they are set, or java applets if your site uses them, or are maybe being disallowed by company A.V. settings.
If so, then, yes, I'd consider that the domain name could be the problem.
If it just isn't appropriate for workplace use (for example, it has some recreational orientation) then I don't think it's appropriate to try to get around workplace restrictions.