Office Connector and Windows authentication

Hi, We have Aras + Office connector installed. Office Connector worked ok until we turned Windows Authentication/Single Sign On to the server. Windows Authentication works ok for normal Aras login, but when Office connector is contacting Aras - it doesn't allow users in. Office connector is still asking password (and it is able to read the Database list - so it has connection to the server), but it doesn't let users in (gives 'Authentication failed for [username]'. I have gone though Office Connector manuals & Windows authentication manuals - but couldn't find any reference to this situation. Should it work in the first place? Any hints how to start resolving this issue? Cheers, Jukka.