I've gone into the Directory Utility on the mac, clicked on the services tab, entered the Active Directory Domain and Computer ID, clicked the Bind button and it showed a little status label which flickered through 5 of 5 steps and then said "An unknown error occurred".

If I ignore the error and just click the OK button further down the screen and make sure the Active Directory service is ticked in the list of services, then go to the Directory Servers tab and try to add an Active Directory by entering my ad domain, computer id, admin username and password I get an error "Unable to add the domain. An unexpected error of type -14090 (eDSAuthFailed) occurred."

Any ideas?